Metal Insulator Transition Creative Research Center

Daejeon, South Korea

Metal Insulator Transition Creative Research Center

Daejeon, South Korea

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Goldflam M.D.,University of California at San Diego | Liu M.K.,University of California at San Diego | Chapler B.C.,University of California at San Diego | Stinson H.T.,University of California at San Diego | And 13 more authors.
Applied Physics Letters | Year: 2014

We demonstrate an electrolyte-based voltage tunable vanadium dioxide (VO2) memory metasurface. Large spatial scale, low voltage, non-volatile switching of terahertz (THz) metasurface resonances is achieved through voltage application using an ionic gel to drive the insulator-to-metal transition in an underlying VO2 layer. Positive and negative voltage application can selectively tune the metasurface resonance into the "off" or "on" state by pushing the VO2 into a more conductive or insulating regime respectively. Compared to graphene based control devices, the relatively long saturation time of resonance modification in VO2 based devices suggests that this voltage-induced switching originates primarily from electrochemical effects related to oxygen migration across the electrolyte-VO2 interface. © 2014 AIP Publishing LLC.


Choi J.,Pukyong National University | Kim B.-J.,Mobrik Co. | Seo G.,KAIST | Kim H.-T.,Metal Insulator Transition Creative Research Center | And 2 more authors.
Current Applied Physics | Year: 2016

We investigated the magnetic field-dependent Hall effect and the thermopower in VO2 thin films at various temperatures by using physical property measurement systems. From the ordinary Hall effect measured at 300-370 K, it was found that the Hall voltage decreased with increasing magnetic field, attributed to the weakening of strong electron correlation, and dominant charge carriers were changed implying the existence of mixed phases near the critical temperature of VO2. A gradual thermopower increase and its sign inversion with increasing temperature gradient were observed at 320-350 K, which seems to stem from percolation processes during the phase transition in VO2. © 2015 Elsevier B.V. All rights reserved.


Liu M.,University of California at San Diego | Liu M.,State University of New York at Stony Brook | Sternbach A.J.,University of California at San Diego | Wagner M.,University of California at San Diego | And 24 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (∼20nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations, but also leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain- and symmetry-dependent mesoscopic phase inhomogeneity are also discussed. These results set the stage for a comprehensive understanding of complex energy landscapes that may not be readily determined by macroscopic approaches. © 2015 American Physical Society.


Maaroof A.I.,Seoul National University | Cho D.-G.,Seoul National University | Kim B.-J.,Metal Insulator Transition Creative Research Center | Kim H.-T.,Metal Insulator Transition Creative Research Center | And 2 more authors.
Journal of Physical Chemistry C | Year: 2013

Hybrid nanostructure-based VO2 semishells (SSs) and Au nanohemispheres (NHs) were developed as a tunable plasmonic nanostructrue. The hybrid structures exhibited an enhanced optical absorbance due to a strong plasmonic coupling between VO2 SSs and Au NHs compared to that of the VO2 SSs alone. Furthermore, its absorption peak can be controlled by the phase transition of VO2 SS under different temperature conditions. The simulation results showed the enhanced plasmonic coupling near the edges of Au NHs, indicating the hemispherical shape of our Au nanostructures can be advantageous in achieving the enhanced plasmonic coupling in our hybrid structures. These "smart" functions of the hybrid nanostructures should provide great opportunities in the development of various optical devices, such as photothermal nanoregulators and ultrafast optical switches. © 2013 American Chemical Society.


Choi J.,Metal Insulator Transition Creative Research Center | Seo G.,Korean University of Science and Technology | Lee Y.W.,Korea University | Kim B.-J.,Metal Insulator Transition Creative Research Center | And 4 more authors.
Technical Digest - 2012 17th Opto-Electronics and Communications Conference, OECC 2012 | Year: 2012

We have studied the magneto-optic Kerr effect (MOKE) of MnGeP 2 films grown by using molecular beam epitaxy (MBE) and prepared in different phosphorus ambiences. Both reflection high energy electron diffraction (RHEED) and 0-20 X-ray diffraction confirm epitaxial growth. We have observed the P pressure dependency in MOKE hysteresis. © 2012 IEEE.


Seo G.,Korean University of Science and Technology | Seo G.,Metal Insulator Transition Creative Research Center | Kim B.-J.,Metal Insulator Transition Creative Research Center | Choi J.,Metal Insulator Transition Creative Research Center | And 3 more authors.
Technical Digest - 2012 17th Opto-Electronics and Communications Conference, OECC 2012 | Year: 2012

In a closed loop circuit connecting a voltage source, a resistor, and a VO 2 device in series, the bistability of the voltage across the device was investigated with respect to a variety of optical illumination powers. © 2012 IEEE.


Liu M.K.,Boston University | Pardo B.,Boston University | Zhang J.,Boston University | Qazilbash M.M.,University of California at San Diego | And 8 more authors.
Physical Review Letters | Year: 2011

Using time-resolved far-infrared spectroscopy, we observe multiple routes for photoinduced phase transitions in V2O3. This includes (i)a photothermal antiferromagnetic to paramagnetic transition and (ii)an incipient strain-generated paramagnetic metal to paramagnetic insulator transition, which manifests as coherent oscillations in the far-infrared conductivity. The ∼100ps conductivity oscillation results from coherent acoustic phonon modulation of the bandwidth W. Our results indicate that poor metals are particularly amenable to coherent strain control of their electronic properties. © 2011 American Physical Society.


Rathi S.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee I.-Y.,Sungkyunkwan Advanced Institute of Nanotechnology | Park J.-H.,Sungkyunkwan Advanced Institute of Nanotechnology | Kim B.-J.,Metal Insulator Transition Creative Research Center | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2014

(Figure Presented) In order to investigate the metal-insulator transition characteristics of VO2 devices annealed in reducing atmosphere after device fabrication at various temperature, electrical, chemical, and thermal characteristics are measured and analyzed. It is found that the sheet resistance and the insulator-metal transition point, induced by both voltage and thermal, decrease when the devices are annealed from 200 to 500 °C. The V 2p3/2 peak variation in X-ray photoelectron spectroscopy (XPS) characterization verifies the reduction of thin-films. A decrease of the transition temperature from voltage hysteresis measurements further endorse the reducing effects of the annealing on VO2 thin-film. © 2014 American Chemical Society.


Seo G.,Metal Insulator Transition Creative Research Center | Seo G.,Korean University of Science and Technology | Kim B.-J.,Korean University of Science and Technology | Wook Lee Y.,Pukyong National University | And 2 more authors.
Applied Physics Letters | Year: 2012

In order to investigate bistable switching characteristics of planar junction devices based on vanadium dioxide (VO 2) thin films, we have measured the optical power dependence of the threshold voltage of the device, at which a current jump, regarded as the Mott metal-insulator transition (MIT), happened, by using an infrared laser with a wavelength of ∼1.55 μm, illuminated onto the VO 2 film. In a test closed loop circuit connecting a DC voltage source, a standard resistor, and a VO 2 thin film device in series, the bistability of the voltage across the device (V D) was examined with respect to a variety of illumination powers (P Ls). By triggering the forward or reverse phase transition (Mott MIT) of the VO 2 film with SET or RESET optical pulse, respectively, the photo-assisted bistable switching of V D in the test circuit properly DC biased could be realized at an intermediate P L chosen between optical powers of SET and RESET pulses. In particular, the transient response of V D showed not only bistable states of V D but also their switching speed. © 2012 American Institute of Physics.


Seo G.,Metal Insulator Transition Creative Research Center | Seo G.,Korean University of Science and Technology | Kim B.-J.,Metal Insulator Transition Creative Research Center | Choi J.,Metal Insulator Transition Creative Research Center | And 3 more authors.
Applied Physics Express | Year: 2012

We experimentally investigated a DC voltage bias effect on laser-induced switching bistability observed in vanadium dioxide (VO 2) thin film through the illumination of the film with a laser at ~1.55 μm. The bias effect on the bistable switching was examined in a circuit composed of a VO 2-based device, DC voltage source, and resistor. At different bias values, static and transient responses of the circuit current were observed by varying illumination power. Specific bias voltages could change the bistable switching into irreversible unidirectional switching, thereby requiring the proper selection of the bias voltage for the stable operation of the bistable switching. © 2012 The Japan Society of Applied Physics.

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