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Halle/Saale, Germany

The Max Planck Institute of Microstructure Physics at Halle is a research institute in Germany in the field of material research. It was founded in 1992 as a follow up of the Academy of Science Institute of Solid State Physics and Electron Microscopy and moved into the new buildings between 1997 and 1999. It is one of 80 institutes in the Max Planck Society .The institute has three main departments:The Theory Department, headed by Prof. Eberhard Gross, mainly carries out theoretical research on the electronic, magnetic, optical, and electrical properties of micro- and nanostructured solid-state systems'.The Experimental Department 1, headed by Prof. Jürgen Kirschner, mainly deals with the magnetic properties of dimensionally reduced systems and their dependence on electronic structure, crystalline structure and morphology.The Experimental Department 2, headed by Prof. Ulrich Gösele, is focussed on the scientific understanding, design and fabrication of new materials for information, communication, engineering as well as bio-technological applications.↑ ↑ ↑ Wikipedia.

Breitenstein O.,Max Planck Institute of Microstructure Physics
Solar Energy Materials and Solar Cells

By evaluating four lock-in thermography images of a solar cell taken at four different biases and an independently measured series resistance image, images of all local two-diode parameters are obtained. Assuming the local validity of the two-diode model, this information enables the construction of local and global dark and illuminated characteristics and of realistic images of local solar cell parameters like efficiency, fill factor, and open circuit voltage with a good spatial resolution. Within this procedure, an injection-dependent lifetime may be regarded by assuming an ideality factor larger than unity for the diffusion current. The possibilities and limitations of this approach are discussed and selected results on a typical industrial multicrystalline cell are introduced. The proposed procedure is a valuable tool for judging which local defects are especially harmful for degrading the fill factor or the open circuit voltage, respectively, and extrapolating the properties of a cell where certain types of defects are excluded. A general limitation of this approach is that it assumes an individual but constant series resistance to each pixel, which neglects the distributed character of the series resistance. © 2012 Elsevier B.V. All rights reserved. Source

Breitenstein O.,Max Planck Institute of Microstructure Physics
Solar Energy Materials and Solar Cells

By evaluating dark lock-in thermography images taken at one reverse and three forward biases, images of all two-diode-parameters J01, J 02, n (ideality factor of J02), and Gp (the parallel Ohmic conductivity) of the dark currentvoltage characteristic are obtained. A local series resistance is explicitly considered and may be provided as a series resistance image, e.g. resulting from luminescence imaging. The results enable a separate investigation of factors influencing the depletion region recombination current and the diffusion current, which is governed by the bulk lifetime. Local IV characteristics of special sites may be simulated. © 2011 Elsevier B.V. All rights reserved. Source

Carrier lifetime in photoelectric processes is the average time an excited carrier is free before recombining or trapping. Lifetime is directly related to defects and it is a key parameter in analyzing photovoltaic effects in semiconductors. We show here a scanning probe method combined with photoinduced current spectroscopy that allows mapping with nanoscale resolution of the generation and recombination lifetimes. Using this method we have analyzed the mechanism of the abnormal photovoltaic effect in multiferroic bismuth ferrite, BiFeO 3. We found that generation and recombination lifetimes in BiFeO 3 are large due to complex generation and recombination processes that involve shallow energy levels in the band gap. The domain walls do not play a major role in the photovoltaic mechanism. © 2012 American Chemical Society. Source

Profeta G.,University of LAquila | Profeta G.,Max Planck Institute of Microstructure Physics | Calandra M.,French National Center for Scientific Research | Mauri F.,French National Center for Scientific Research
Nature Physics

Graphene is the physical realization of many fundamental concepts and phenomena in solid-state physics. However, in the list of graphene's many remarkable properties, superconductivity is notably absent. If it were possible to find a way to induce superconductivity, it could improve the performance and enable more efficient integration of a variety of promising device concepts including nanoscale superconducting quantum interference devices, single-electron superconductor-quantum dot devices, nanometre-scale superconducting transistors and cryogenic solid-state coolers. To this end, we explore the possibility of inducing superconductivity in a graphene sheet by doping its surface with alkaline metal adatoms, in a manner analogous to which superconductivity is induced in graphite intercalated compounds (GICs). As for GICs, we find that the electrical characteristics of graphene are sensitive to the species of adatom used. However, contrary to what happens in GICs, Li-covered graphene is superconducting at a much higher temperature with respect to Ca-covered graphene. © 2012 Macmillan Publishers Limited. All rights reserved. Source

Zakeri K.,Max Planck Institute of Microstructure Physics
Physics Reports

Elementary spin excitations (magnons) play a fundamental role in condensed matter physics, since many phenomena e.g.magnetic ordering, electrical (as well as heat) transport properties, ultrafast magnetization processes, and most importantly electron/spin dynamics can only be understood when these quasi-particles are taken into consideration. In addition to their fundamental importance, magnons may also be used for information processing in modern spintronics.Here the concept of spin excitations in ultrathin itinerant magnets is discussed and reviewed. Starting with a historical introduction, different classes of magnons are introduced. Different theoretical treatments of spin excitations in solids are outlined. Interaction of spin-polarized electrons with a magnetic surface is discussed. It is shown that, based on the quantum mechanical conservation rules, a magnon can only be excited when a minority electron is injected into the system. While the magnon creation process is forbidden by majority electrons, the magnon annihilation process is allowed instead. These fundamental quantum mechanical selection rules, together with the strong interaction of electrons with matter, make the spin-polarized electron spectroscopies as appropriate tools to excite and probe the elementary spin excitations in low-dimensional magnets e.g ultrathin films and nanostructures. The focus is put on the experimental results obtained by spin-polarized electron energy loss spectroscopy and spin-polarized inelastic tunneling spectroscopy. The magnon dispersion relation, lifetime, group and phase velocity measured using these approaches in various ultrathin magnets are discussed in detail. The differences and similarities with respect to the bulk excitations are addressed. The role of the temperature, atomic structure, number of atomic layers, lattice strain, electronic complexes and hybridization at the interfaces are outlined. A possibility of simultaneous probing of magnons and phonons in complex low-dimensional ferromagnetic oxide nanostructures is discussed. The influence of the relativistic spin-orbit coupling on high-energy magnons is addressed. It is shown how the spin-orbit coupling breaks the energy degeneracy of the magnons excited in an ultrathin ferromagnet, and how it influences their lifetime, amplitude, group and phase velocity. A potential application of these new effects in modern spintronics is outlined. It is illustrated how one can take advantage of collective nature of magnons and use these quasi-particles for probing the magnetic exchange interaction at buried interfaces. © 2014 Elsevier B.V. Source

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