야구 토토PHYSICS/BK21 SEMINAR[09.08.20]
관련링크
본문
"Two-dimensional semimetaland excitonic insulator
Ø야구 토토Speaker :야구 토토 Dr.야구 토토Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø야구 토토Place : Physics Seminar Room (Science Bldg, 3-201)
Ø야구 토토Date & Time :야구 토토Aug, 20 (Thu), 15:00 ~ 16:00 pm
Abstract
The talk is devoted to the results of the experimental study of a principally new 2D electron system: a two-dimensional (2D) semimetal,야구 토토recently야구 토토realized for야구 토토the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in야구 토토wide야구 토토(thickness of 18 nm – 21 nm) undoped HgTe QWs with야구 토토the야구 토토reduced야구 토토symmetry야구 토토surfaces (such as (013)야구 토토and (112)).야구 토토Because야구 토토of야구 토토an inverted band structure and respectively the peculiar properties of야구 토토size야구 토토quantization야구 토토in야구 토토these야구 토토QWs야구 토토the overlap of a conductance band (with the bottom in the centre of Brillouin zone) and valence band (with the few maximums in its side points) arises. Its value is about 10 meV. So due to this overlap we have the true 2D semimetal similar to that of classical 3D semimetals such as Bi, Sb or As and there is the opportunity to realize the simultaneous existence of an equilibrium gas or liquid of 2D electrons and 2D holes.야구 토토Moreover by means of the field effect transistor structure fabricated on the basis of QW we are야구 토토able야구 토토by야구 토토means야구 토토of simple changing of야구 토토the야구 토토gate야구 토토voltage,야구 토토firstly,야구 토토to야구 토토realize야구 토토and야구 토토study야구 토토transition야구 토토2D야구 토토electron야구 토토metal – 2D semimetal – 2D hole metal and, secondly,야구 토토2D semimetallic야구 토토state with any ratio between the densities야구 토토of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their야구 토토simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron야구 토토mobility야구 토토jump야구 토토due야구 토토to야구 토토hole야구 토토screening야구 토토of야구 토토electron야구 토토scattering야구 토토by야구 토토impurities, 3)야구 토토anomalous temperature dependence of 2D semimetal resistance because of electron scattering by heavy holes. It is likely this effect is the first clear demonstration of the야구 토토direct야구 토토influence야구 토토of야구 토토a야구 토토particle-particle야구 토토inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion야구 토토principal.야구 토토But야구 토토the야구 토토most exiting opportunity appearing due to realization of 2D semimetal is to carry out야구 토토the야구 토토direct야구 토토experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one야구 토토of야구 토토the야구 토토greatest야구 토토20 century condense matter physicists sir Nevill Mott. In 1961 he considered a semimetal and assumed that the Coulomb interaction between electrons and holes have to lead to the formation of their bound야구 토토state and a semimetal should become an insulator. It is surprising but till now this very interesting and important transition has not been directly observed. The main reason of this situation is that till the last야구 토토time야구 토토there was absent the system in which this transition could be realized and then야구 토토directly야구 토토fixed야구 토토by야구 토토resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did야구 토토not야구 토토fit야구 토토because야구 토토of야구 토토the absence of the simple procedure to change the density of electron and holes. So in our 2D semimetal the EI state induced by magnetic field is found. It arises between electron-like and hole-like quantum Hall liquid states at the point Ns = Ps and near it. It야구 토토is야구 토토shown야구 토토that야구 토토the야구 토토transition야구 토토metal – EI야구 토토is야구 토토similar야구 토토to superconductor-normal metal transition and described by BCS (Bardeen-Coopper-Schrieffer)-scenario: up to the critical temperature Tc ≈ 1 K no temperature dependence of the야구 토토transport야구 토토and야구 토토capacitance response of the system is야구 토토observed야구 토토but just야구 토토below야구 토토this야구 토토temperature야구 토토the야구 토토strong야구 토토insulator야구 토토behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,야구 토토hjlee@postech.ac.kr)
"
Ø야구 토토Speaker :야구 토토 Dr.야구 토토Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø야구 토토Place : Physics Seminar Room (Science Bldg, 3-201)
Ø야구 토토Date & Time :야구 토토Aug, 20 (Thu), 15:00 ~ 16:00 pm
Abstract
The talk is devoted to the results of the experimental study of a principally new 2D electron system: a two-dimensional (2D) semimetal,야구 토토recently야구 토토realized for야구 토토the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in야구 토토wide야구 토토(thickness of 18 nm – 21 nm) undoped HgTe QWs with야구 토토the야구 토토reduced야구 토토symmetry야구 토토surfaces (such as (013)야구 토토and (112)).야구 토토Because야구 토토of야구 토토an inverted band structure and respectively the peculiar properties of야구 토토size야구 토토quantization야구 토토in야구 토토these야구 토토QWs야구 토토the overlap of a conductance band (with the bottom in the centre of Brillouin zone) and valence band (with the few maximums in its side points) arises. Its value is about 10 meV. So due to this overlap we have the true 2D semimetal similar to that of classical 3D semimetals such as Bi, Sb or As and there is the opportunity to realize the simultaneous existence of an equilibrium gas or liquid of 2D electrons and 2D holes.야구 토토Moreover by means of the field effect transistor structure fabricated on the basis of QW we are야구 토토able야구 토토by야구 토토means야구 토토of simple changing of야구 토토the야구 토토gate야구 토토voltage,야구 토토firstly,야구 토토to야구 토토realize야구 토토and야구 토토study야구 토토transition야구 토토2D야구 토토electron야구 토토metal – 2D semimetal – 2D hole metal and, secondly,야구 토토2D semimetallic야구 토토state with any ratio between the densities야구 토토of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their야구 토토simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron야구 토토mobility야구 토토jump야구 토토due야구 토토to야구 토토hole야구 토토screening야구 토토of야구 토토electron야구 토토scattering야구 토토by야구 토토impurities, 3)야구 토토anomalous temperature dependence of 2D semimetal resistance because of electron scattering by heavy holes. It is likely this effect is the first clear demonstration of the야구 토토direct야구 토토influence야구 토토of야구 토토a야구 토토particle-particle야구 토토inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion야구 토토principal.야구 토토But야구 토토the야구 토토most exiting opportunity appearing due to realization of 2D semimetal is to carry out야구 토토the야구 토토direct야구 토토experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one야구 토토of야구 토토the야구 토토greatest야구 토토20 century condense matter physicists sir Nevill Mott. In 1961 he considered a semimetal and assumed that the Coulomb interaction between electrons and holes have to lead to the formation of their bound야구 토토state and a semimetal should become an insulator. It is surprising but till now this very interesting and important transition has not been directly observed. The main reason of this situation is that till the last야구 토토time야구 토토there was absent the system in which this transition could be realized and then야구 토토directly야구 토토fixed야구 토토by야구 토토resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did야구 토토not야구 토토fit야구 토토because야구 토토of야구 토토the absence of the simple procedure to change the density of electron and holes. So in our 2D semimetal the EI state induced by magnetic field is found. It arises between electron-like and hole-like quantum Hall liquid states at the point Ns = Ps and near it. It야구 토토is야구 토토shown야구 토토that야구 토토the야구 토토transition야구 토토metal – EI야구 토토is야구 토토similar야구 토토to superconductor-normal metal transition and described by BCS (Bardeen-Coopper-Schrieffer)-scenario: up to the critical temperature Tc ≈ 1 K no temperature dependence of the야구 토토transport야구 토토and야구 토토capacitance response of the system is야구 토토observed야구 토토but just야구 토토below야구 토토this야구 토토temperature야구 토토the야구 토토strong야구 토토insulator야구 토토behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,야구 토토hjlee@postech.ac.kr)
"
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