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News Article | August 22, 2016
Site: news.mit.edu

MIT Physics Department Senior Research Scientist Jagadeesh S. Moodera was one of the pioneers in the field of spin-polarized magnetic tunnel junctions, which led to a thousand-fold increase in hard disk storage capacity. Using his group’s expertise working with atomically thin materials that exhibit exotic features, Moodera is laying a step-by-step foundation toward a new generation of quantum computers. Moodera’s group is making progress toward devices that display resistance-free, spin-polarized electrical current; memory storage at the level of single molecules; and capture the elusive paired electron “halves” known as Majorana fermions, which are sought after as qubits for quantum computing. This work combines materials that allow the free flow of electrons only on their surface (topological insulators) with other materials that lose their resistance to electricity (superconductors). Researchers call mixed layers of these materials heterostructures. A key goal is to push these effects up from ultracold temperatures to ordinary temperatures for everyday use. “Our group specializes in the growth and understanding the physical phenomena at the atomic level of any number of exotic combinations of these materials plus heterostructures with different other materials such as ferromagnetic layers or superconductors and so on,” Moodera says. Majorana fermions, which can be thought of as a paired “electron halves,” may lead to creating quantum entanglement believed necessary for quantum computers. “Our first goal is to look for the Majorana fermions, unambiguously detect them, and show this is it. It’s been the goal for many people for a long time. It’s one of those things predicted 80 years ago, and yet to be shown in a conclusive manner,” Moodera says. Moodera’s group is searching for these Majorana fermions on the surface of gold, a phenomenon predicted in 2012 by William and Emma Rogers Professor of Physics Patrick Lee and Andrew C. Potter PhD ’13. “I have a lot of hope that it’s going to come up with something very interesting, this particular area is exotically rich,” Moodera says. His team reported progress toward this goal in a Nano Letters paper published on March 4. Postdoc Peng Wei, with fellow Moodera group postdocs Ferhat Katmis and Cui-Zu Chang, demonstrate that epitaxial (111)-oriented gold thin films become superconducting when grown on top of superconducting vanadium film. The vanadium becomes a superconductor below 4 kelvins, which is hundreds of degrees below room temperature. Tests show that the surface state of (111)-oriented gold also becomes superconducting, which holds out potential for this system in the search for Majorana fermions. Future work will seek to detect Majorana fermions on the ends of (111)-oriented gold nanowires. “In this kind of nanowire, in principle, we would expect Majorana fermion states to exist at the end of the nanowire instead of in the middle,” Wei explains. Moodera says, “We have not discovered Majorana fermions yet, however, we have made a very nice foundation for that.” Further results will be published soon. In a series of 2015 papers, Moodera’s group demonstrated the first reported truly zero-resistance edge current in the quantum anomalous Hall state of a topological insulator system, realizing a 1988 prediction by F. Duncan M. Haldane at Princeton University. The importance of comprehensive achievements of perfect quantum anomalous Hall state at zero magnetic field as well as the demonstration of dissipationless chiral edge current in a topological insulator is well brought out in a Journal Club for Condensed Matter Physics commentary by Harvard University Professor Bertrand I. Halperin, a pioneer in the field. “In this system, there is a very special edge state. The bulk is insulating, but the edge is metallic,” says Cui-Zu Chang, lead author of the Nature Materials paper and Physical Review Letters paper published in April and July 2015. “Our group is the first to show a completely dissipationless edge state, meaning that the resistance for current flow exactly becomes zero when the quantum state is reached at low temperatures,” Chang says. “If one can realize this effect, for example, at room temperature, it will be remarkably valuable. You can use this kind of effect to develop quantum electronics including the quantum computer,” Chang says. “In this kind of computer, there is minimal heating effect; the current flow is completely dissipationless; and you can also communicate over very long distance.” In a 2013 paper with collaborators from Northeastern University, Göttingen University in Germany and Spence High School in New York, Moodera and MIT postdoc Bin Li demonstrated a superconducting spin switch in a structure sandwiching an aluminum layer between europium sulfide layers. In this work, the intrinsic magnetization of europium sulfide controls superconductivity in the aluminum layer. The direction of magnetization in europium sulfide can be reversed, which can thereby switch the aluminum between superconducting and normal states, making it potentially useful for logic circuits and nonvolatile memory applications a step in the direction of superconducting spintronics. These experiments validated a theoretical prediction 50 years ago by French Nobel Laureate Pierre-Gilles deGennes. Several years ago Guoxing Miao, then a junior researcher with Moodera, observed a unique energy profile across a sandwich structure made with metallic islands confined within two europium sulfide magnetic insulator barriers. This arrangement of the inherent large energy separation in the nano islands combined with the large interfacial magnetic field confined at the interface and the spin selective transmission property of the adjacent europium sulfide powerfully modifies the two-dimensional electronic structures. They observed spin-assisted charge transfer across such a device, generating a spontaneous spin current and voltage. These unique properties can be practical for controlling spin flows in electronic devices and for energy harvesting. Published in Nature Communications in April 2014, these were unexpected fundamental results, Moodera says. Guoxing Miao is an assistant professor at University of Waterloo and Institute for Quantum Computing in Canada. More recently, the researchers paired europium sulfide with graphene, creating a strong edge current, which they reported March 28 in Nature Materials. “What we find is very exciting,” postdoc Peng Wei, lead author of the paper, says: “Experiments show a strong magnetic field (more than 14 Tesla) experienced by graphene originating in the europium sulfide that polarizes the spins of electrons in the graphene layer without affecting the orbital motion of the electrons.” In the device, europium sulfide produces a large field, called a magnetic exchange field, which raises the energy of spin-up electrons and lowers the energy of spin-down electrons in graphene and creates an edge current with spin-up electrons streaming in one direction and spin-down electrons streaming in the opposite direction. These effects are brought about by the confinement of electrons in these atomically thin devices, fellow postdoc Ferhat Katmis explains. At the interface between europium sulfide, which is a magnetic insulator, and graphene, Peng Wei explains, the graphene can “feel” the huge exchange field, or internal magnetism, which can reach millions times bigger than the Earth’s magnetic field, from the europium sulfide. This effect is potentially useful for spin-based memory and logic devices and possibly quantum computing. Moodera was a guest editor of the July 2014 MRS Bulletin, which highlighted progress in organic spintronics. Controlling magnetic behavior at the interface of the materials is again the key element in this approach. By adding magnetic sensing capability to these large organic molecules (up to hundreds of atoms per molecule), their magnetic orientation can be switched back and forth. This work holds promise to serve as photo-switches, color displays, and information storage units at the molecular level. These molecules can start out completely non-magnetic, but when they are placed on the surface of a magnetic material, their behavior changes. “They share electrons at the interface. These molecules share some of their electrons into the ferromagnetic layer or the ferromagnetic layer actually gives out some of its electrons carrying with it the magnetic behavior,” Moodera explains. Electrons from the magnetic material carry a magnetic signature, which influences the organic molecule to switch between resistive and conductive states. This collaborative work between researchers in the U.S., Germany, and India was published as a Nature Letter paper in 2013. Moodera and co-inventor Karthik V. Raman PhD ’11 were issued a patent in May 2014 for high-density molecular memory storage. It is one of four patents issued to Moodera and colleagues. “We have shown early stages of such a possibility of these molecules being used for storing information,” Moodera says. “This is what we want to explore. This will allow us to store information in molecules in the future.” He projects that molecular storage can increase storage density by 1,000 to 10,000 times compared to current technology. “That gives you an idea of how powerful it can become,” he says. Organic molecules have other advantages as well, he says, including lower cost, less energy consumption, flexibility and more environmentally friendly materials. “But it’s a very, very huge area, almost untapped direction where many unprecedented new phenomena might emerge if it can be patiently investigated fundamentally,” he cautions. Moodera is currently seeking long-term funding for this research into permanent memory devices using magnetic single molecules. “It’s a visionary program which means somebody has to be patient,” Moodera explains. “We are quite capable of doing this here if we get good support. ... Everything has to be looked at and understood, and then go further, so there is no set a priori recipe for this!” In 2009, Moodera and two MIT colleagues (the late Robert Meservey and Paul Tedrow, then group leader) shared the Oliver E. Buckley Condensed Matter Prize from the American Physical Society with Terunobu Miyazaki from Tohuku University in Japan for "pioneering work in the field of spin-dependent tunneling and for the application of these phenomena to the field of magnetoelectronics (also called spintronics)." “Jagadeesh Moodera and team were the first to show magnetoresistance from a magnetic tunnel junction at room temperature — a fundamental discovery that has enabled rapid growth of data storage capacity. All hard disk drives made since 2005 have a MTJ as the read sensor,” says Tiffany Santos ’02, PhD ’07, a former Moodera lab member who now works as a principal research engineer at HGST in San Francisco. As a materials science undergraduate and then doctoral student in Moodera's group, Santos explored spin-polarized tunneling in MTJs made of novel materials such as magnetic semiconductors and organic molecules. Santos was awarded best thesis prize from the Department of Materials Science and Engineering both for her BS and PhD theses. In common bar magnets, which have north and south poles, two magnets are attracted if opposite poles face, but will repel if the same poles face each other. Similarly, in a magnetic tunnel junction, the current flow across the layered materials will behave differently depending on whether the magnetism of the layers points in the same, or in the opposite, direction — either resisting the flow of current or enhancing it. This spin tunneling work, which dates to the 1990s, revealed that pairing two thin magnetic materials separated by a thin insulator causes electrons to move, or “quantum tunnel,” through the insulator from one magnet to the other, which is why it is called a magnetic tunnel junction. “This change in the current flow, very significant, can be detected very easily,” Moodera says. Since these magnetic materials are atomically thin, rather than north and south poles, their magnetism is associated with the up or down spin of electrons, which is a quantum property, and they are characterized as parallel when their spins are in alignment, or antiparallel when their spins point in the opposite directions. “So all you have to do is change from parallel to anti-parallel orientation, and there you have this beautiful spin sensor, or spin memory,” Moodera says. “This spin memory is non-volatile; that’s the most striking thing about it. You can set this particular device in a particular orientation, leave it alone, after a million years it’ll be still like that; meaning that the information which is stored here will be permanent.” Institute Professor Mildred S. Dresselhaus has known Moodera for many years, initially through his work using magnetic fields for materials research. Moodera, she says, developed expertise in spin phenomena long before they became popular topics in science and he has attained similar status in topological insulators. “His career has been all like that. He works for the love of science, and he’s not particularly interested in recognition,” Dresselhaus adds. Although Moodera has never been a faculty member, he works effectively with students and he finds his own support, she notes. “MIT is a place that can accommodate people like him,” Dresselhaus says. Limited funding means the U.S. is in danger of losing its leadership role in research, Moodera fears. He involves high school students and undergraduates (nearly 150 so far) in his research, many becoming coauthors in the publications and patents. “When we tell the young students and postdocs, ‘Oh, physics is wonderful, you should get into research, you really can discover many things that are exciting and valuable’, we are not actually telling the whole story. Despite funding support from National Science Foundation and Office of Naval Research for our program, there is increasing uncertainty and pressure to raise research funds. ... With constant struggle for funds, one spends much time in dealing with these issues. ... We wish there is reliable and continuous support when the track record is good. Science is like art — if creative breakthroughs are needed, then the proper support should be there with long-term vision, with freedom to explore, and without breaks and uncertainties. When one looks at some of the breakthroughs we have achieved so far — magnetic tunnel junctions that drives all hard drives in computers, prototype molecular spin memory, nonvolatile perfect superconducting spin memory/switch or even the latest totally spin-polarized edge current which is perfectly dissipationless, evidently the foundations for tomorrow’s cutting edge technology, isn’t it crystal clear that such a research program be unequivocally supported to benefit our society?” he asks. Despite his lab’s prominence in spintronics and topological insulators, making further progress in the current research environment means he depends on federal and other outside grants. “If I don’t have funding, I close the shop,” he says. “Everything moves so fast, you cannot wait for tomorrow. Everything has to happen today, that’s the unfortunate thing dealing with uncertainty. It’s a lot of pressure and stress on us, particularly in the last 10 years. The funding situation has become so volatile that we are kept under the dark cloud, constantly concerned about what is coming next.” Yet the situation has not always been so. During a tour of his lab facilities, Moodera recalls a phone call (over 20 years ago) from an Office of Naval Research (ONR) program director, Krystl Hathaway, who suggested there was money available, his work was high-quality, and that he should apply. “That was when I had only a month or two of funds left to sustain a research program! So, I said yes! I couldn’t believe it in the beginning,” he recalls. “I put in a one-page application. In a week’s time she sent me the money to tidy me out for four months. After that, I put in a real, several-page proposal for a full grant, and she supported my research program for over 10 years. Two years after this support started, research led to the discovery of the phenomenon called the tunnel magnetoresistance in 1994-95, which besides creating a vast new area of research, is also instrumental in the explosion of unbelievable storage capacity and speed in computer hard drives as we enjoy today at rock bottom cost. Most notable is that this work was mainly done with a summer high school intern who later joined MIT [Lisa Kinder, '99] and an undergraduate [Terrilyn Wong '97].” Later, when the same program officer was at a Materials Research Society (MRS) meeting in Boston, she visited Moodera’s lab and noticed the age of a key piece of thin film equipment used in creating the tunnel magnetoresistance breakthrough. It was then about 35 years old and had been cobbled together mostly from salvaged parts. Again she volunteered to provide substantial funding to build specialized equipment for a technique called molecular beam epitaxy (MBE), which is used to create ultra-clean thin films, atomic layer by atomic layer. On vacation in India, Moodera got a phone call from a physics administrator (the late Margaret O'Meara), telling him Hathaway from ONR was urgently looking for him. “I came back the next day, and then I spent four hours writing a proposal, which another two hours later was submitted from MIT. It all happened in one day essentially, and one week later I got $350,000, which built our first MBE system,” he says. “It’s a very versatile system that even after 20 years continues to deliver big results in the growth and investigation of the field of quantum coherent materials at present. By carefully planning and optimizing we even got some other critical parts that we needed for our other equipment in the lab.” “Dr. Hathaway, and then subsequently Dr. Chagaan Baatar, the new program director at ONR, were very happy that we produced a lot more things in the new system. It made a huge difference in our program. So that’s how sometimes it works out, and fundamental research should be supported if one looks for breakthroughs!” he says. “People come in and see, 'these people need support'. So that kind of thing should happen now, I think.” Funding for basic science has to increase by manyfold, Moodera suggests. “The future is actually created and defined now. Evidently it’s very important then. If you don’t invest now, there is no future development. A vision for fundamental knowledge buildup is strongly eroding in the country now, and thus needs to be corrected before it reaches the point of no return,” he says. Moodera has been at MIT for over three decades, where his group is part of the Francis Bitter Magnet Laboratory (which is now under Plasma Science and Fusion Center) and the Department of Physics. Moodera’s lab equipment ranges from the newest two-story scanning tunneling microscope that can examine atomic surfaces and molecules under extreme cold and high magnetic fields to a 1960s’ vintage glass liquid helium cryostat, which still sees frequent use. “It’s not the equipment. It’s how you think about a problem and solve it, that’s our way of looking at things. ... We train real scientists here; ones that can really think, come up with something out of essentially nothing. To start from basic atoms and molecules and actually build things, completely new and understand the emerging phenomena; unexpected science can come out of it,” Moodera says. “This group has solved important physics in ferromagnetism,” postdoc Peng Wei says. “We actually have very unique equipment that cannot be seen in other labs.” A native of Bangalore, India, Moodera plays badminton, ping-pong, and tennis, and he follows world tennis, soccer, and cricket. With his wife, MIT Department of Materials Science and Engineering senior lecturer Geetha Berera, Moodera likes to hike and enjoy nature. His hobbies include gardening and bird watching.


Paul Woskov is collecting rocks. A growing number of granite and basalt squares perch on cabinet tops and shelves around his office, each a record of his latest experiment in drilling. Some show clean circles that fully penetrate the rock, while others hold glassy craters. Woskov, a senior research engineer at MIT’s Plasma Science and Fusion Center (PSFC), is using a gyrotron, a specialized radio-frequency (RF) wave generator developed for fusion research, to explore how millimeter RF waves can open holes through hard rock by melting or vaporizing it. Penetrating deep into hard rock is necessary to access virtually limitless geothermal energy resources, to mine precious metals, or explore new options for nuclear waste storage. But it is a difficult and expensive process, and today’s mechanical drilling technology has limitations. Woskov believes that powerful millimeter-wave sources could increase deep hard rock penetration rates by more than ten times at lower cost over current mechanical drilling systems, while providing other practical benefits. “There is plenty of heat beneath our feet,” he says, “something like 20 billion times the energy that the world uses in one year.” But, Woskov notes, most studies of the accessibility of geothermal energy are based on current mechanical technology and its limitations. They do not consider that a breakthrough advance in drilling technology could make possible deeper, less expensive penetration, opening into what Woskov calls “an enormous reserve of energy, second only to fusion: base energy, available 24/7.” Current rotary technology is a mechanical grinding process that is limited by rock hardness, deep pressures, and high temperatures. Specially designed “drilling mud,” pumped through the hollow drill pipe interior, is used to enable deep drilling and to remove the excess cuttings, returning them to the surface via the ring-shaped space between the drill pipe and borehole wall. The pressure of the mud also keeps the hole from collapsing, sealing, and strengthening the hole in the process. But there is a limit to the pressures such a borehole can withstand, and typically holes cannot be drilled beyond 30,000 feet (9 km). Woskov asks, “What if you could drill beyond this limit? What if you could drill over 10 kilometers into the Earth’s crust?” With his proposed gyrotron technology this is theoretically possible. Woskov laughs when he reveals that drilling engineers have a hard time believing his technology does not use the costly drilling mud they depend on. But, he explains, with a gyrotron, high-temperature physics will replace the mechanical functions of low-temperature mud, allowing drillers to extract rock matter through vaporization or displace the melt through pressurization. Similarly, the high temperature melted rock will seal the walls of the borehole, and the high pressure from the increased temperature will prevent collapse. In principle, because an increase in temperature in a confined volume will always result in an increase in pressure over local pressure, drillers could maintain the stability of a borehole to greater depths than possible with drilling muds. Woskov observes yet another advantage: “Our beams don’t need to be round. Forces underground are anisotropic — not symmetrical. That is one reason holes collapse. But we can shape our beam to respond to local pressures. You can create an elliptical hole with the major axis corresponding to the anisotropy of the forces, essentially recovering the strength of a round hole in a symmetrical force field.” Later this spring, the researcher is planning to move his base of operation from the PSFC to the Air Force Research Lab (AFRL) in Kirkland, New Mexico, in order to take advantage of a microwave source that would allow him to perform experiments at a power level a factor of 10 higher than is currently possible in the laboratory at MIT. He would be able to graduate from drilling rocks in the 4-6 inch range to those in the 2-4 feet range. He is especially interested in exploring how well the rock can be vaporized, which would only be possible with the higher power available at AFRL. Support for this project originally came from MIT Energy Initiative (MITEI), which in 2008 provided seed money and later a follow-up grant. Although Woskov continues to pursue ways his technology can advance geothermal energy research, his current support is from the Department of Energy's Office of Nuclear Science, through Impact Technologies LLC, which funds him to explore deep bore hole storage of radioactive and nuclear wastes. At 6 km deep, such bore holes would place waste much farther from the biosphere than is possible with near-earth depositories such as Yucca Mountain. The bottom 2 kilometers of the hole would hold waste, capped with a 2-km seal — which is currently considered the “weak link” in the process. Woskov is experimenting with melted basalt and the more viscous granite to learn how he can seal the holes with melted rock, which could provide the most secure entombment of the waste products. Woskov, who joined MIT’s Francis Bitter Magnet Laboratory in 1976 before becoming a founding member of the Plasma Fusion Center in 1979, is approaching his 40th anniversary at MIT. The first three decades of his tenure focused heavily on high-power far infrared scattering for measuring energy distribution of fast ions, the product of fusion reactions. The exploration took much longer than anyone anticipated, but when it eventually found success in Europe on the TEXTOR tokamak reactor, Woskov was left looking for a new direction. While still pursuing fusion, he began exploring some spinoff technologies that could be realized in a matter of years rather than decades. He received one R&D 100 Award after another for a series of projects: a thermometer for measuring temperatures in high-temperature furnaces; a hazardous waste emissions monitor for incinerators and power pants; a device to monitor molten metals: all experiments that used developments in fusion research to address shorter-term problems. “Occasionally you have to do something that has a near-term reward,” Woskov laughs, noting that it can be frustrating when you work on something for 30 years without a final product. The beauty that long-term fusion research has provided the technology for so many exciting short-term projects is not lost on Woskov. And he notes with amusement that so much fusion research revolves around protecting materials in fusion devices from being damaged by hot plasma, while his current project exploits the high energy of fusion technology to see how effectively it can melt materials. Woskov foresees a number of other uses for the microwave technology. The high-temperature pressures of microwaves could be used to break apart rocks for mining, or excavate rock to create tunnels and canals. It could also be used for fracking in place of pressurized water, which is controversial due to its limited supply and resulting water contamination. “Energy trumps matter,” Woskov proclaims, excited by how microwave heat and pressure could literally move mountains, or at least pieces of them. For now he’s going to continue melting his way through the earth’s crust, one rock at a time.


News Article | April 14, 2016
Site: www.theenergycollective.com

Paul Woskov is collecting rocks. A growing number of granite and basalt squares perch on cabinet tops and shelves around his office, each a record of his latest experiment in drilling. Some show clean circles that fully penetrate the rock, while others hold glassy craters. Woskov, a senior research engineer at MIT’s Plasma Science and Fusion Center (PSFC), is using a gyrotron, a specialized radio-frequency (RF) wave generator developed for fusion research, to explore how millimeter RF waves can open holes through hard rock by melting or vaporizing it. Penetrating deep into hard rock is necessary to access virtually limitless geothermal energy resources, to mine precious metals, or explore new options for nuclear waste storage. But it is a difficult and expensive process, and today’s mechanical drilling technology has limitations. Woskov believes that powerful millimeter-wave sources could increase deep hard rock penetration rates by more than ten times at lower cost over current mechanical drilling systems, while providing other practical benefits. “There is plenty of heat beneath our feet,” he says, “something like 20 billion times the energy that the world uses in one year.” But, Woskov notes, most studies of the accessibility of geothermal energy are based on current mechanical technology and its limitations. They do not consider that a breakthrough advance in drilling technology could make possible deeper, less expensive penetration, opening into what Woskov calls “an enormous reserve of energy, second only to fusion: base energy, available 24/7.” Current rotary technology is a mechanical grinding process that is limited by rock hardness, deep pressures, and high temperatures. Specially designed “drilling mud,” pumped through the hollow drill pipe interior, is used to enable deep drilling and to remove the excess cuttings, returning them to the surface via the ring-shaped space between the drill pipe and borehole wall. The pressure of the mud also keeps the hole from collapsing, sealing, and strengthening the hole in the process. But there is a limit to the pressures such a borehole can withstand, and typically holes cannot be drilled beyond 30,000 feet (9 km). Woskov asks, “What if you could drill beyond this limit? What if you could drill over 10 kilometers into the Earth’s crust?” With his proposed gyrotron technology this is theoretically possible. Woskov laughs when he reveals that drilling engineers have a hard time believing his technology does not use the costly drilling mud they depend on. But, he explains, with a gyrotron, high-temperature physics will replace the mechanical functions of low-temperature mud, allowing drillers to extract rock matter through vaporization or displace the melt through pressurization. Similarly, the high temperature melted rock will seal the walls of the borehole, and the high pressure from the increased temperature will prevent collapse. In principle, because an increase in temperature in a confined volume will always result in an increase in pressure over local pressure, drillers could maintain the stability of a borehole to greater depths than possible with drilling muds. Woskov observes yet another advantage: “Our beams don’t need to be round. Forces underground are anisotropic — not symmetrical. That is one reason holes collapse. But we can shape our beam to respond to local pressures. You can create an elliptical hole with the major axis corresponding to the anisotropy of the forces, essentially recovering the strength of a round hole in a symmetrical force field.” Later this spring, the researcher is planning to move his base of operation from the PSFC to the Air Force Research Lab (AFRL) in Kirkland, New Mexico, in order to take advantage of a microwave source that would allow him to perform experiments at a power level a factor of 10 higher than is currently possible in the laboratory at MIT. He would be able to graduate from drilling rocks in the 4-6 inch range to those in the 2-4 feet range. He is especially interested in exploring how well the rock can be vaporized, which would only be possible with the higher power available at AFRL. Support for this project originally came from MIT Energy Initiative (MITEI), which in 2008 provided seed money and later a follow-up grant. Although Woskov continues to pursue ways his technology can advance geothermal energy research, his current support is from the Department of Energy’s Office of Nuclear Science, through Impact Technologies LLC, which funds him to explore deep bore hole storage of radioactive and nuclear wastes. At 6 km deep, such bore holes would place waste much farther from the biosphere than is possible with near-earth depositories such as Yucca Mountain. The bottom 2 kilometers of the hole would hold waste, capped with a 2-km seal — which is currently considered the “weak link” in the process. Woskov is experimenting with melted basalt and the more viscous granite to learn how he can seal the holes with melted rock, which could provide the most secure entombment of the waste products. Woskov, who joined MIT’s Francis Bitter Magnet Laboratory in 1976 before becoming a founding member of the Plasma Fusion Center in 1979, is approaching his 40th anniversary at MIT. The first three decades of his tenure focused heavily on high-power far infrared scattering for measuring energy distribution of fast ions, the product of fusion reactions. The exploration took much longer than anyone anticipated, but when it eventually found success in Europe on the TEXTOR tokamak reactor, Woskov was left looking for a new direction. While still pursuing fusion, he began exploring some spinoff technologies that could be realized in a matter of years rather than decades. He received one R&D 100 Award after another for a series of projects: a thermometer for measuring temperatures in high-temperature furnaces; a hazardous waste emissions monitor for incinerators and power pants; a device to monitor molten metals: all experiments that used developments in fusion research to address shorter-term problems. “Occasionally you have to do something that has a near-term reward,” Woskov laughs, noting that it can be frustrating when you work on something for 30 years without a final product. The beauty that long-term fusion research has provided the technology for so many exciting short-term projects is not lost on Woskov. And he notes with amusement that so much fusion research revolves around protecting materials in fusion devices from being damaged by hot plasma, while his current project exploits the high energy of fusion technology to see how effectively it can melt materials. Woskov foresees a number of other uses for the microwave technology. The high-temperature pressures of microwaves could be used to break apart rocks for mining, or excavate rock to create tunnels and canals. It could also be used for fracking in place of pressurized water, which is controversial due to its limited supply and resulting water contamination. “Energy trumps matter,” Woskov proclaims, excited by how microwave heat and pressure could literally move mountains, or at least pieces of them. For now he’s going to continue melting his way through the earth’s crust, one rock at a time.


News Article | October 19, 2016
Site: www.theenergycollective.com

Pablo Rodriguez Fernandez is hunched over a computer in the control room of MIT’s fusion reactor, gathering data that will inform the design of a new one — a device that could solve the world’s energy problems. He is surrounded by other scientists running simulations and analyzing data. Their work is spread across tables and desks covered in computers and a chaos of wires. The objective: to design a machine that will harness the same energy process that powers the sun and deliver it to the world, carbon free. They are here to make fusion energy a reality. This is the headquarters of a MIT’s Alcator C-Mod. A fixture on campus for 23 years, C-Mod uses high-intensity magnetic fields to confine hot plasma in a donut-shaped chamber — a reactor design known as a tokamak, a transliteration of a Russian word for “toroidal chamber.” During C-Mod’s final run, the reactor’s team of operators will take MIT’s high pressure world record to an extraordinary new level. It will create renewed hope that a faster path to clean and safe energy is before us. On this day in mid-September, as Fernandez and his fellow graduate students in the Department of Nuclear Science and Engineering type, calculate, and predict, the machine is operating on the other side of a nearby concrete wall. Fernandez, along with PhD candidates Alex Creely and Juan Ruiz Ruiz, have joined research scientist Nathan Howard to run a code that combines plasma measurements from several tokamaks, including C-Mod, into a single model. They have worked on other tokamaks, such as NSTX at the Princeton Plasma Physics Lab, ASDEX-Upgrade at the Max Planck Institute in Germany, and DIII-D at General Atomics in San Diego. All of them are world-class facilities, but C-Mod’s atmosphere is special, say Creely and Fernandez, who are in shorts and sneakers. “It’s less formal at MIT than at the national labs,” says Fernandez. His t-shirt reads, “Changing the World.” Despite its apparently casual atmosphere, C-Mod has also established stringent safety standards that have been widely exported across the MIT campus. That balance between rigor and flexibility, says Creely, is part of what has made C-Mod such a success. “This is one of the most powerful machines in the world, and graduate students can go in and work, build diagnostics and such, on our own time,” he says. “People are open to you attaching new things and making modifications. It’s just this awesome university feel here,” he adds. He nods toward the scientists with legs draped over the backs of office chairs, the bike helmets, water bottles, Coke cans, and the student lab equipment decorated, in some instances, with beer logos and political slogans. “We have people from physics, aero-astro, nuclear engineering, wherever. All this expertise in one location. And you can just go talk to people.” Indeed, even before its final experiment changed the debate over field intensity and materials, the world of fusion science owed a great debt to C-Mod. The machine has been at the heart of energy experiments that have shaped the careers of hundreds of scientists and engineers. It has inspired almost 200 doctoral theses, dynamic collaborations, and scientific breakthroughs. It has been the training ground for a whole generation of plasma scientists. “We’re not just doing science.” Anne White and her students are striking a campy, dramatic pose for a group photograph. They are in a hallway outside of the control room creating a commemorative record of their time together in the reactor complex on Albany Street. Hanging on the wall behind them are the protective hard hats that are required when entering C-Mod territory. Many of them are personalized with last names. These, too, are on the way to becoming mementoes. White, the Ida and Cecil Green Professor in Nuclear Engineering, and her team of students are international leaders in assessing and refining the mathematical models used in fusion reactor design. With the closure of C-Mod, White says, she has arranged intensive collaborations with other groups worldwide. These relationships will be key for their research continuing and moving forward. Later the same afternoon, she and John Rice, a senior research scientist, talk openly about the shutdown. Rice has been at MIT for 45 years. During that time, three Alcator machines have come and gone, but C-Mod will be the last in this line. “I’m probably one of the last people to accept the situation,” Rice says. “I still can’t believe next Friday is going to be the last day.” The two of them are from different generations. White more formal in a tailored outfit with her blonde hair up in a bun, a pencil stuck through it. Rice with his long gray hair braided down his back in a look reminiscent of the 70s. MIT fusion scientists, they agree, will maintain a broad experimental portfolio and connections to friends around the world. “We will keep having an impact on the science,” says White. “Students will get a chance to do awesome stuff and write lots of papers and go through the training we think is so important for fusion scientists.” In 2012, the Department of Energy (DOE) announced the end of funding for the reactor. The White House had decided to invest instead in the International Thermonuclear Experimental Reactor (ITER), which is under construction in France, a project that draws directly from design and materials advances made in C-Mod. Although MIT’s fusion experiment was slated for elimination in both the 2013 and 2014 fiscal budgets, broad-based advocacy efforts managed to keep it alive until this month. Government players are at odds when it comes to supporting fusion research. The White House wants to see a 9.2 percent reduction in the DOE’s $438 million Fusion Sciences Program in 2017. Senate appropriators would cut it even further to $280 million­ — but zero out contributions to ITER and redistribute the money to other energy programs. The House, meanwhile, wants to boost the program spending by 2.7 percent but contribute the bulk — $125 million — to ITER. It may be many months before lawmakers reach clarity on fusion research spending in the U.S. Now, with the closure looming, Rice is trying to make the best of it. “We have data analysis left to do. We have plans for the future. We have great people who work well together — and we intend to continue to move fusion forward,” he says. Listening from a few computer terminals away, team member Norman Cao, a graduate student in the nuclear department, adds: “Fusion is a cool place to be. We’re not just doing science. We’re trying to apply it to the real world.” In his office across the street, Martin Greenwald, deputy director of MIT’s Plasma Science and Fusion Center, is working hard to get new projects off the ground. The closure of C-Mod is the end of a chapter but it’s not the end of the story, he says. “These machines have their own lifetime. They start, we do research, and they end. Our work will continue.” Many of the most influential concepts in fusion science have been developed at MIT, says Greenwald. Recently, he came across a 1971 patent for the first of the Alcator machines. Then, as now, the project was focusing on a high-magnetic-field approach to fusion. Indeed the fusion program, born in the early 70s, is a direct result of the synergy between MIT physicists and engineers at the Francis Bitter Magnet Laboratory, which is part of the Plasma Science and Future Center. “Our magnet group invented an approach to superconducting magnets that is essentially the default today. It’s used by all the big machines in fusion,” says Greenwald. “Now we want to develop magnet technology further.” There is good reason. Fusion reactions are slow until the fuel is heated to unimaginably high temperatures, “over 100 million degrees — far hotter than the core of the sun,” says Greenwald. Then electrons in the fuel atoms are stripped of their nuclei and the gas becomes a plasma, the fourth state of matter. At these temperatures, magnetic fields are the only reliable way to insulate hot plasma from material walls of the reactor. “We’ve attained the necessary plasma densities and temperatures in C-Mod,” says Greenwald. “But Alcator reactors are relatively small. They produce about as much fusion power as they consume.” Figuring out how to yield net energy production out of a fusion reactor is really the heart of what researchers are pursuing now. The creation of a giant tokamak such as ITER is a massive endeavor. The international effort is projected to exceed $50 billion, which is 10 times the original estimate. Fueled experiments will not begin before 2027 — already more than a decade behind schedule. There might be alternatives to “going big,” says Greenwald. He describes the MIT-student designed “Affordable, Robust, Compact” (ARC) reactor design proposal, which calls for a smaller, more modular reactor that relies on advances in materials and magnet technology. Such a tokamak could be built at one-tenth the size and cost. To begin, MIT will seek private funding. The Advanced Diverter Experiment, or ADX, is a project MIT would like to develop in parallel. It would be roughly the same size as C-Mod but use a different design. It would tackle several important problems for fusion by enabling researchers to learn more about the behavior of hot plasmas, their interactions with material surfaces, and the behavior of structural materials in a fusion environment. MIT has proposed that the Department of Energy fund it. Greenwald says the easy joke is that fusion energy is the power source of the future — and always will be. But he believes otherwise. “There is a lot of energy and excitement here about what we could do moving forward. We can hit a home run if we can just get up to bat.” Ten years ago, Dennis Whyte came to MIT in large part because of its fusion program. More specifically, he came because he saw that students were combining their classroom learning with hands-on training at a world-class fusion facility. Today about a third of C-Mod’s experimental leaders are students, says Whyte, head of the Deaprtment of Nuclear Science and Engineering and director of the Plasma Science and Fusion Center. “Young people are driving the innovations. They are rethinking old assumptions and really making us think about new ways that we can get to fusion,” he says. “They are changing how research is done in the modern age.” The relative youth of the faculty members in Whyte’s department supports his observation. Nine out of 17 are under the age of 40. “The drive that comes from this new generation of fusion scientists is immense,” Whyte says. “Just a few years ago, it did not seem as if we’d be able to make net energy possible.” With a new generation of superconducting materials and a design path blazed by Alcator C-Mod, which firmly established the advantage of using high magnetic fields to achieve fusion energy, “suddenly we have an opportunity to develop extremely compact and very efficient devices,” he says. “This is what makes MIT great. We get these young people in here and we empower them to actually rethink standard assumptions and try to make the world better through their dedication and talent. And they do it.” Back in the control room, Earl Marmar glances toward several large display screens that entirely cover a front wall. They show him the tokamak is operating at full parameters. Head of the Alcator C-Mod project since 2002, Marmar is not holding the machine back. There was a time he was hesitant to run the reactor at its highest magnetic fields for fear of stressing it. Those days are over. “For the last few years, we’ve really pushed hard. We’ve learned new things as a result, and we haven’t broken the machine,” he says. “Even now we have new ideas coming. We’re still running for another week. It’s not over yet.” He says the federal government provided funds to put C-Mod into a safe shutdown state. “It will be in a condition where we could bring it back up to life in the future. Although there is no plan to do that right now. We are heading in new directions.” The lived-in feel of the control room speaks to the kind of familiarity the scientists, engineers, and students have developed with the machine, and with each other. Over by her team, Anne White speaks with Howard, who says graduate students have benefited greatly from the opportunity to work directly on a tokamak. “We’re doing these collaborations but there is just nothing like having your own machine. Losing it is a sad state of affairs. But we’ll take our skill set that we’ve honed here and apply it to other tokamaks.” Including ones the team hopes to design and build at MIT. On its final day of operations, C-Mod was still breaking new scientific ground. That morning, the team operating the reactor broke the world record for plasma pressure achieved in a magnetically confined field. The pressure inside C-Mod was 2.05 atmospheres — better, by a factor of 2, than every other tokamak in the world. And these other reactors, which are 20 to 100 times larger in volume than C-Mod, are dwarfed by the scale of ITER, which will be 800 times the volume of C-Mod. The key difference, says Whyte, is the underlying technology driving C-Mod. “High-magnetic fields are the way to go,” he says. “You couldn’t ask for a more compelling demonstration of how ready our science is for high-field fusion. Even a project on the scale of ITER is only projected to achieve 2.8 atmospheres — and that’s 20 years from now!” As MIT was celebrating its unprecedented success, Whyte’s fusion-science colleagues at Princeton University were lamenting a loss. Earlier in the same week, they learned that their recently upgraded reactor would be offline for up to a year due to a coil malfunction, leaving only one major fusion research reactor in operation in the U.S. The situation poses yet another challenge to scientific advancement, but Whyte is undeterred. “We have assembled an incredible science and engineering team,” says Whyte. The openness to new ideas and the collaborative ethos that have powered so many of the C-Mod results will go on, he says. “Our students are using their research and applying it. You can feel the excitement. We want that optimism to reach the community more broadly. We want to get our vision out to the whole world. Let’s accelerate fusion.”


News Article | October 14, 2016
Site: news.mit.edu

Pablo Rodriguez Fernandez is hunched over a computer in the control room of MIT’s fusion reactor, gathering data that will inform the design of a new one — a device that could solve the world’s energy problems. He is surrounded by other scientists running simulations and analyzing data. Their work is spread across tables and desks covered in computers and a chaos of wires. The objective: to design a machine that will harness the same energy process that powers the sun and deliver it to the world, carbon free. They are here to make fusion energy a reality. This is the headquarters of a MIT’s Alcator C-Mod. A fixture on campus for 23 years, C-Mod uses high-intensity magnetic fields to confine hot plasma in a donut-shaped chamber — a reactor design known as a tokamak, a transliteration of a Russian word for “toroidal chamber.” During C-Mod’s final run, the reactor’s team of operators will take MIT’s high pressure world record to an extraordinary new level. It will create renewed hope that a faster path to clean and safe energy is before us. On this day in mid-September, as Fernandez and his fellow graduate students in the Department of Nuclear Science and Engineering type, calculate, and predict, the machine is operating on the other side of a nearby concrete wall. Fernandez, along with PhD candidates Alex Creely and Juan Ruiz Ruiz, have joined research scientist Nathan Howard to run a code that combines plasma measurements from several tokamaks, including C-Mod, into a single model. They have worked on other tokamaks, such as NSTX at the Princeton Plasma Physics Lab, ASDEX-Upgrade at the Max Planck Institute in Germany, and DIII-D at General Atomics in San Diego. All of them are world-class facilities, but C-Mod’s atmosphere is special, say Creely and Fernandez, who are in shorts and sneakers. “It’s less formal at MIT than at the national labs,” says Fernandez. His t-shirt reads, “Changing the World.” Despite its apparently casual atmosphere, C-Mod has also established stringent safety standards that have been widely exported across the MIT campus. That balance between rigor and flexibility, says Creely, is part of what has made C-Mod such a success. “This is one of the most powerful machines in the world, and graduate students can go in and work, build diagnostics and such, on our own time,” he says. “People are open to you attaching new things and making modifications. It’s just this awesome university feel here,” he adds. He nods toward the scientists with legs draped over the backs of office chairs, the bike helmets, water bottles, Coke cans, and the student lab equipment decorated, in some instances, with beer logos and political slogans. “We have people from physics, aero-astro, nuclear engineering, wherever. All this expertise in one location. And you can just go talk to people.” Indeed, even before its final experiment changed the debate over field intensity and materials, the world of fusion science owed a great debt to C-Mod. The machine has been at the heart of energy experiments that have shaped the careers of hundreds of scientists and engineers. It has inspired almost 200 doctoral theses, dynamic collaborations, and scientific breakthroughs. It has been the training ground for a whole generation of plasma scientists. “We’re not just doing science.” Anne White and her students are striking a campy, dramatic pose for a group photograph. They are in a hallway outside of the control room creating a commemorative record of their time together in the reactor complex on Albany Street. Hanging on the wall behind them are the protective hard hats that are required when entering C-Mod territory. Many of them are personalized with last names. These, too, are on the way to becoming mementoes. White, the Ida and Cecil Green Professor in Nuclear Engineering, and her team of students are international leaders in assessing and refining the mathematical models used in fusion reactor design. With the closure of C-Mod, White says, she has arranged intensive collaborations with other groups worldwide. These relationships will be key for their research continuing and moving forward. Later the same afternoon, she and John Rice, a senior research scientist, talk openly about the shutdown. Rice has been at MIT for 45 years. During that time, three Alcator machines have come and gone, but C-Mod will be the last in this line. “I’m probably one of the last people to accept the situation,” Rice says. “I still can’t believe next Friday is going to be the last day.” The two of them are from different generations. White more formal in a tailored outfit with her blonde hair up in a bun, a pencil stuck through it. Rice with his long gray hair braided down his back in a look reminiscent of the 70s. MIT fusion scientists, they agree, will maintain a broad experimental portfolio and connections to friends around the world. “We will keep having an impact on the science,” says White. “Students will get a chance to do awesome stuff and write lots of papers and go through the training we think is so important for fusion scientists.” In 2012, the Department of Energy (DOE) announced the end of funding for the reactor. The White House had decided to invest instead in the International Thermonuclear Experimental Reactor (ITER), which is under construction in France, a project that draws directly from design and materials advances made in C-Mod. Although MIT’s fusion experiment was slated for elimination in both the 2013 and 2014 fiscal budgets, broad-based advocacy efforts managed to keep it alive until this month. Government players are at odds when it comes to supporting fusion research. The White House wants to see a 9.2 percent reduction in the DOE’s $438 million Fusion Sciences Program in 2017. Senate appropriators would cut it even further to $280 million­ — but zero out contributions to ITER and redistribute the money to other energy programs. The House, meanwhile, wants to boost the program spending by 2.7 percent but contribute the bulk — $125 million — to ITER. It may be many months before lawmakers reach clarity on fusion research spending in the U.S. Now, with the closure looming, Rice is trying to make the best of it. “We have data analysis left to do. We have plans for the future. We have great people who work well together — and we intend to continue to move fusion forward,” he says. Listening from a few computer terminals away, team member Norman Cao, a graduate student in the nuclear department, adds: “Fusion is a cool place to be. We’re not just doing science. We’re trying to apply it to the real world.” In his office across the street, Martin Greenwald, deputy director of MIT's Plasma Science and Fusion Center, is working hard to get new projects off the ground. The closure of C-Mod is the end of a chapter but it’s not the end of the story, he says. “These machines have their own lifetime. They start, we do research, and they end. Our work will continue.” Many of the most influential concepts in fusion science have been developed at MIT, says Greenwald. Recently, he came across a 1971 patent for the first of the Alcator machines. Then, as now, the project was focusing on a high-magnetic-field approach to fusion. Indeed the fusion program, born in the early 70s, is a direct result of the synergy between MIT physicists and engineers at the Francis Bitter Magnet Laboratory, which is part of the Plasma Science and Future Center. “Our magnet group invented an approach to superconducting magnets that is essentially the default today. It’s used by all the big machines in fusion,” says Greenwald. “Now we want to develop magnet technology further.” There is good reason. Fusion reactions are slow until the fuel is heated to unimaginably high temperatures, “over 100 million degrees — far hotter than the core of the sun,” says Greenwald. Then electrons in the fuel atoms are stripped of their nuclei and the gas becomes a plasma, the fourth state of matter. At these temperatures, magnetic fields are the only reliable way to insulate hot plasma from material walls of the reactor. “We’ve attained the necessary plasma densities and temperatures in C-Mod,” says Greenwald. “But Alcator reactors are relatively small. They produce about as much fusion power as they consume.” Figuring out how to yield net energy production out of a fusion reactor is really the heart of what researchers are pursuing now. The creation of a giant tokamak such as ITER is a massive endeavor. The international effort is projected to exceed $50 billion, which is 10 times the original estimate. Fueled experiments will not begin before 2027 — already more than a decade behind schedule. There might be alternatives to “going big,” says Greenwald. He describes the MIT-student designed “Affordable, Robust, Compact” (ARC) reactor design proposal, which calls for a smaller, more modular reactor that relies on advances in materials and magnet technology. Such a tokamak could be built at one-tenth the size and cost. To begin, MIT will seek private funding. The Advanced Diverter Experiment, or ADX, is a project MIT would like to develop in parallel. It would be roughly the same size as C-Mod but use a different design. It would tackle several important problems for fusion by enabling researchers to learn more about the behavior of hot plasmas, their interactions with material surfaces, and the behavior of structural materials in a fusion environment. MIT has proposed that the Department of Energy fund it. Greenwald says the easy joke is that fusion energy is the power source of the future — and always will be. But he believes otherwise. “There is a lot of energy and excitement here about what we could do moving forward. We can hit a home run if we can just get up to bat.” Ten years ago, Dennis Whyte came to MIT in large part because of its fusion program. More specifically, he came because he saw that students were combining their classroom learning with hands-on training at a world-class fusion facility. Today about a third of C-Mod’s experimental leaders are students, says Whyte, head of the Deaprtment of Nuclear Science and Engineering and director of the Plasma Science and Fusion Center. “Young people are driving the innovations. They are rethinking old assumptions and really making us think about new ways that we can get to fusion,” he says. “They are changing how research is done in the modern age.” The relative youth of the faculty members in Whyte’s department supports his observation. Nine out of 17 are under the age of 40. “The drive that comes from this new generation of fusion scientists is immense,” Whyte says. “Just a few years ago, it did not seem as if we’d be able to make net energy possible.” With a new generation of superconducting materials and a design path blazed by Alcator C-Mod, which firmly established the advantage of using high magnetic fields to achieve fusion energy, “suddenly we have an opportunity to develop extremely compact and very efficient devices,” he says. “This is what makes MIT great. We get these young people in here and we empower them to actually rethink standard assumptions and try to make the world better through their dedication and talent. And they do it.” Back in the control room, Earl Marmar glances toward several large display screens that entirely cover a front wall. They show him the tokamak is operating at full parameters. Head of the Alcator C-Mod project since 2002, Marmar is not holding the machine back. There was a time he was hesitant to run the reactor at its highest magnetic fields for fear of stressing it. Those days are over. “For the last few years, we’ve really pushed hard. We’ve learned new things as a result, and we haven’t broken the machine,” he says. “Even now we have new ideas coming. We’re still running for another week. It’s not over yet.” He says the federal government provided funds to put C-Mod into a safe shutdown state. “It will be in a condition where we could bring it back up to life in the future. Although there is no plan to do that right now. We are heading in new directions.” The lived-in feel of the control room speaks to the kind of familiarity the scientists, engineers, and students have developed with the machine, and with each other. Over by her team, Anne White speaks with Howard, who says graduate students have benefited greatly from the opportunity to work directly on a tokamak. “We’re doing these collaborations but there is just nothing like having your own machine. Losing it is a sad state of affairs. But we’ll take our skill set that we’ve honed here and apply it to other tokamaks.” Including ones the team hopes to design and build at MIT. On its final day of operations, C-Mod was still breaking new scientific ground. That morning, the team operating the reactor broke the world record for plasma pressure achieved in a magnetically confined field. The pressure inside C-Mod was 2.05 atmospheres — better, by a factor of 2, than every other tokamak in the world. And these other reactors, which are 20 to 100 times larger in volume than C-Mod, are dwarfed by the scale of ITER, which will be 800 times the volume of C-Mod. The key difference, says Whyte, is the underlying technology driving C-Mod. “High-magnetic fields are the way to go,” he says. “You couldn’t ask for a more compelling demonstration of how ready our science is for high-field fusion. Even a project on the scale of ITER is only projected to achieve 2.8 atmospheres — and that’s 20 years from now!” As MIT was celebrating its unprecedented success, Whyte’s fusion-science colleagues at Princeton University were lamenting a loss. Earlier in the same week, they learned that their recently upgraded reactor would be offline for up to a year due to a coil malfunction, leaving only one major fusion research reactor in operation in the U.S. The situation poses yet another challenge to scientific advancement, but Whyte is undeterred. “We have assembled an incredible science and engineering team,” says Whyte. The openness to new ideas and the collaborative ethos that have powered so many of the C-Mod results will go on, he says. “Our students are using their research and applying it. You can feel the excitement. We want that optimism to reach the community more broadly. We want to get our vision out to the whole world. Let’s accelerate fusion.”


News Article | August 22, 2016
Site: news.mit.edu

Laptop computer users operating their devices on their laps will be familiar with the heat they generate, which comes from electrical resistance converting waste energy to heat. Scientists dream of creating electronic devices with little or no resistance to the flow of electricity, in order to reduce heat output, save energy, and extend device capabilities. In the last several years theorists and experimentalists have been trying to achieve this goal using extremely thin materials with special physical properties, called topological insulators (TIs). Recently there has been a breakthrough towards this goal: Dissipationless flow of current has been achieved in TIs when it enters a quantum state without any external magnetic fields — although, as of now, only at extremely low temperatures, its potential can be significant if the operating temperature could be raised. Topological insulators allow the free flow of electrons only on their surface while blocking the flow of electrons through their bulk. MIT postdoc Cui-Zu Chang, then a doctoral student at Tsinghua University in China, and colleagues at Chinese Academy of Sciences-Institute of Physics, Tsinghua, and Stanford University, reported the experimental demonstration of electrons flowing only along the edge of a topological insulator film circuit, driven by an internal magnetic field, which physicists call the quantum anomalous Hall effect. To provide internal magnetism for their circuit, they added chromium to their material, which was composed of bismuth, antimony, and tellurium. However, the Tsinghua system still showed remnants of electrical resistance to the edge current, frustratingly close to zero resistance. Improving upon his earlier work, Chang and colleagues in the group of Jagadeesh Moodera, along with collaborators from Penn State, Stanford and Northeastern University, achieved robust quantum anomalous Hall state and near dissipationless electron transport in topological insulators. Chang and colleagues at MIT replaced chromium with vanadium to obtain atomically thin layers of their magnetic topological insulators. They stacked sample films of this material on a base of strontium titanate. They reported early results of this work in Nature Materials in May 2015, achieving very slight resistance to current flowing lengthwise along their sample. Via local and nonlocal measurements, Chang and colleagues at MIT and Penn State University with further optimization achieved zero resistance to current flowing lengthwise along the edge of their sample circuit at the extremely low temperature of 25 millikelvins (0.025 kelvins), a state physicists call “dissipationless chiral edge transport.” This lack of resistance is independent of length, they say in a Physical Review Letters paper published in July 2015. Moodera’s group is part of the Francis Bitter Magnet Laboratory and MIT Department of Physics. “In this system, there is a very special edge channel,” Chang explains. “The bulk is insulating but the chiral edge channel is metallic and spin polarized, so it’s very useful for the next generation electronics and spintronics with low power consumption.” “A signal entering this system can propagate a long distance without losing any of its energy. While presently it can only be realized at very low temperatures, there are indications that this can be raised,” Chang says. Observing this kind of quantum anomalous Hall state below 1 kelvin requires a special piece of equipment called a cryostat, so work continues to produce this effect at a higher temperature. Adding an extra element such as chromium or vanadium to introduce a special property (such as magnetism) to a material is known as doping. The vanadium-doped system showed three distinct advantages over the chromium-doped system: • twofold increase in the temperature above which the material loses magnetism (its Curie temperature), allowing the vanadium system to operate at zero resistance at a slightly higher but still very cold temperature; • 10 times increase in the stability of its intrinsic magnetism (its coercive field); and • one-half reduction in its carrier density. The vanadium system spontaneously shows magnetism at below about 23 kelvins. Results show this quantum anomalous Hall state can survive in a vanadium-doped system up to 5 kelvins (-450 degrees Fahrenheit). However, above 5 kelvins, the effect disappears and the normal resistance of the bulk material appears. While their sample film is still extremely thin — about 4 nanometers — the device studied is about 1 mm long by 0.4 mm wide, which is relatively large compared with other studies of quantum spintronic phenomena. “We make this kind of sample so big to preserve the delicate properties of the film. These films are very sensitive to water and air, which degrades the film properties,” Chang explains. Chang worked for five years in his doctoral studies at Tsinghua University searching for the quantum anomalous Hall effect, which was predicted in 1988 by F. Duncan M. Haldane at Princeton, he notes. “In a recent theoretical paper, no quantum anomalous Hall effect was predicted in a vanadium-doped topological insulator, whereas we experimentally showed the opposite is true, that this system is better for observing quantum anomalous Hall effect!” Chang says. The 2006 discovery of topological insulators made the realization of quantum anomalous Hall effect practical. Chang cites three conditions to realize this effect: atomically flat thin TI film; introducing magnetism into the TI film; and tuning the chemical potential (Fermi level) into the gap induced by magnetism. After an intense search, Chang first observed the quantum anomalous Hall state in Oct. 9, 2012, in a sample of chromium-doped bismuth antimony, simultaneously showing a noticeable decrease in longitudinal resistance, according to a report on the evolution of their work published Feb. 26 in the Journal of Physics: Condensed Matter. Separately, a group at Tokyo University which included Joseph Checkelsky, now assistant professor of physics at MIT, confirmed the Tsinghua work and also observed the quantum anomalous Hall effect in the same system, Chang says. “If you can realize this effect at room temperature, it will significantly change our life. You can use this kind of effect to develop quantum electronics including the quantum computer,” Chang says. “In this kind of computer, there is minimal heating effect; the current flow is completely dissipationless; and you can also communicate over very long distance.” Although a superconductor can also reach zero resistance at low temperature, it is not spin-polarized, so it can transfer only electrical information but not spin information, Chang explains. The advantage of the quantum anomalous Hall effect, or topological edge state, is that the edge current is spin-polarized and robust, so it can be used to transfer information. Chang, 30, is originally from the Chinese kite-making city of Weifang, in Shandong province. He received his bachelor’s in optical engineering at Shandong University in China and doctorate in physics at Tsinghua University. His wife, Jia Song, has a PhD in mathematics from Tsinghua University. Chang’s work is supported by the Center for Integrated Quantum Materials under NSF grant DMR-1231319. A third-year postdoc in the Moodera group, he is looking for a faculty position in the fall.


News Article | October 23, 2015
Site: news.mit.edu

Professor Emeritus Benjamin Lax of the MIT Department of Physics passed away on April 21 at the age of 99. Born December 29, 1915, in Miskolc, Hungary, Lax came to New York City as a boy and received his bachelor’s degree in mechanical engineering from the Cooper Union in 1941. During World War II, Lax enlisted in the U.S. Army, where, after completing officer candidate school and other training, he was assigned to the radar laboratory at MIT. While there, he was in charge of putting together a new radar system, dubbed “Little Abner,” for field testing. After the end of the war, he pursued a PhD degree in plasma physics at MIT, receiving his degree in 1949. He joined the MIT Lincoln Laboratories in 1951, later becoming head of the solid-state physics division in 1958, and associate director of the laboratory in 1964. While at Lincoln Laboratory he made major contributions to the understanding of semiconductors, particularly through studies of their energy band structure using cyclotron resonance. He was also a co-inventor on an early patent for a semiconductor laser. His pioneering work on semiconductors provided an important foundation for the development of semiconductor technology now used in computers, cell phones, and other high-technology devices. In the late 1950s, while working at MIT Lincoln Laboratory, Lax led a group of scientists and engineers who proposed a high magnetic field laboratory on the MIT campus for research in solid-state physics, plasma physics, magnetic resonance spectroscopy, and engineering. The proposal was accepted, the National Magnet Laboratory (NML) was established in 1960, and Lax served as its director for its first 21 years. He also became a professor in the MIT Department of Physics. With Lax at the helm, the NML was an international leader in a remarkably wide range of research areas including the physics of solids in high magnetic fields; high magnetic-field nuclear magnetic resonance: studies of magnetic fields of the brain; and the use of high magnetic fields for plasma physics and magnetic-confinement fusion research. The first high magnetic field tokamak confinement device, Alcator, was constructed and operated at the NML; the results obtained were a major advance in nuclear fusion research. Eventually, the research on plasma physics and fusion energy required a larger facility, leading to the establishment of the MIT Plasma Fusion Center. Lax was also active in teaching and training PhD students. He was a mentor to many young research scientists who gained valuable experience conducting research at the NML and went on to become international leaders in the fields of solid-state and plasma physics. He retired from the directorship of the NML — by then the Francis Bitter National Magnet Laboratory and today the Francis Bitter Magnet Laboratory — in 1981 and from the physics faculty in 1986. Among the honors and awards that he received were the Oliver E. Buckley Prize for condensed matter physics of the American Physical Society in 1960 and election to the National Academy of Sciences. He was the author of over 300 journal articles, and co-author of a classic book on microwave ferrites and ferromagnetics. Following his retirement from the Magnet Laboratory and the physics faculty, he stayed active in physics for more the 15 years, including being a consultant at the MIT Lincoln Laboratory. Lax, who had lived in Newton, Massachusetts, was the husband of the late Blossom Cohen Lax, the father of Daniel R. Lax of Atlanta, and Robert M. Lax of Newton, and the grandfather of Rachael Lax Day.


Sai Sankar Gupta K.B.,Leiden University | Daviso E.,Leiden University | Daviso E.,Francis Bitter Magnet Laboratory | Jeschke G.,ETH Zurich | And 5 more authors.
Journal of Magnetic Resonance | Year: 2014

In solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) MAS NMR experiments, strong signal enhancement is observed from molecules forming a spin-correlated radical pair in a rigid matrix. Two-dimensional 13C-13C dipolar-assisted rotational resonance (DARR) photo-CIDNP MAS NMR experiments have been applied to obtain exact chemical shift assignments from those cofactors. Under continuous illumination, the signals are enhanced via three-spin mixing (TSM) and differential decay (DD) and their intensity corresponds to the electron spin density in pz orbitals. In multiple-13C labelled samples, spin diffusion leads to propagation of signal enhancement to all 13C spins. Under steady-state conditions, direct signal assignment is possible due to the uniform signal intensity. The original intensities, however, are inaccessible and the information of the local electron spin density is lost. Upon laser-flash illumination, the signal is enhanced via the classical radical pair mechanism (RPM). The obtained intensities are related to isotropic hyperfine interactions aiso and both enhanced absorptive and emissive lines can be observed due to differences in the sign of the local isotropic hyperfine interaction. Exploiting the mechanism of the polarization, selectivity can be increased by the novel time-resolved two-dimensional dipolar-assisted rotational resonance (DARR) MAS NMR experiment which simplifies the signal assignment compared to complex spectra of the same RCs obtained by continuous illumination. Here we present two-dimensional time-resolved photo-CIDNP MAS NMR experiments providing both directly: signal assignment and spectral editing by sign and strength of aiso. Hence, this experiment provides a direct key to the electronic structure of the correlated radical pair. © 2014 Elsevier Inc. All rights reserved.


Maly T.,Francis Bitter Magnet Laboratory | Andreas L.B.,Francis Bitter Magnet Laboratory | Smith A.A.,Francis Bitter Magnet Laboratory | Griffin R.G.,Francis Bitter Magnet Laboratory
Physical Chemistry Chemical Physics | Year: 2010

Perdeuteration of biological macromolecules for magic angle spinning solid-state NMR spectroscopy can yield high-resolution 2H- 13C correlation spectra and the method is therefore of great interest for the structural biology community. Here we demonstrate that the combination of sample deuteration and dynamic nuclear polarization yields resolved 2H-13C correlation spectra with a signal enhancement of ε ≥ 700 compared to a spectrum recorded with microwaves off and otherwise identical conditions. To our knowledge, this is the first time that 2H-DNP has been employed to enhance MAS-NMR spectra of a biologically relevant system. The DNP process is studied using several polarizing agents and the technique is applied to obtain 2H-13C correlation spectra of U-[2H, 13C] proline. © 2010 the Owner Societies.

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