PHYSICS/BK21 SEMINAR[09.08.20]
관련링크
본문
"Two-dimensional semimetaland excitonic insulator
Ø바카라 조작Speaker :바카라 조작 Dr.바카라 조작Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø바카라 조작Place : Physics Seminar Room (Science Bldg, 3-201)
Ø바카라 조작Date & Time :바카라 조작Aug, 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,바카라 조작recently바카라 조작realized for바카라 조작the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in바카라 조작wide바카라 조작(thickness of 18 nm – 21 nm) undoped HgTe QWs with바카라 조작the바카라 조작reduced바카라 조작symmetry바카라 조작surfaces (such as (013)바카라 조작and (112)).바카라 조작Because바카라 조작of바카라 조작an inverted band structure and respectively the peculiar properties of바카라 조작size바카라 조작quantization바카라 조작in바카라 조작these바카라 조작QWs바카라 조작the 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.바카라 조작Moreover by means of the field effect transistor structure fabricated on the basis of QW we are바카라 조작able바카라 조작by바카라 조작means바카라 조작of simple changing of바카라 조작the바카라 조작gate바카라 조작voltage,바카라 조작firstly,바카라 조작to바카라 조작realize바카라 조작and바카라 조작study바카라 조작transition바카라 조작2D바카라 조작electron바카라 조작metal – 2D semimetal – 2D hole metal and, secondly,바카라 조작2D semimetallic바카라 조작state with any ratio between the densities바카라 조작of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their바카라 조작simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron바카라 조작mobility바카라 조작jump바카라 조작due바카라 조작to바카라 조작hole바카라 조작screening바카라 조작of바카라 조작electron바카라 조작scattering바카라 조작by바카라 조작impurities, 3)바카라 조작anomalous temperature dependence of 2D semimetal resistance because of electron scattering by heavy holes. It is likely this effect is the first clear demonstration of the바카라 조작direct바카라 조작influence바카라 조작of바카라 조작a바카라 조작particle-particle바카라 조작inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion바카라 조작principal.바카라 조작But바카라 조작the바카라 조작most exiting opportunity appearing due to realization of 2D semimetal is to carry out바카라 조작the바카라 조작direct바카라 조작experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one바카라 조작of바카라 조작the바카라 조작greatest바카라 조작20 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 bound바카라 조작state 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 last바카라 조작time바카라 조작there was absent the system in which this transition could be realized and then바카라 조작directly바카라 조작fixed바카라 조작by바카라 조작resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did바카라 조작not바카라 조작fit바카라 조작because바카라 조작of바카라 조작the 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. It바카라 조작is바카라 조작shown바카라 조작that바카라 조작the바카라 조작transition바카라 조작metal – EI바카라 조작is바카라 조작similar바카라 조작to superconductor-normal metal transition and described by BCS (Bardeen-Coopper-Schrieffer)-scenario: up to the critical temperature Tc ≈ 1 K no temperature dependence of the바카라 조작transport바카라 조작and바카라 조작capacitance response of the system is바카라 조작observed바카라 조작but just바카라 조작below바카라 조작this바카라 조작temperature바카라 조작the바카라 조작strong바카라 조작insulator바카라 조작behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,바카라 조작hjlee@postech.ac.kr)
"
Ø바카라 조작Speaker :바카라 조작 Dr.바카라 조작Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø바카라 조작Place : Physics Seminar Room (Science Bldg, 3-201)
Ø바카라 조작Date & Time :바카라 조작Aug, 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,바카라 조작recently바카라 조작realized for바카라 조작the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in바카라 조작wide바카라 조작(thickness of 18 nm – 21 nm) undoped HgTe QWs with바카라 조작the바카라 조작reduced바카라 조작symmetry바카라 조작surfaces (such as (013)바카라 조작and (112)).바카라 조작Because바카라 조작of바카라 조작an inverted band structure and respectively the peculiar properties of바카라 조작size바카라 조작quantization바카라 조작in바카라 조작these바카라 조작QWs바카라 조작the 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.바카라 조작Moreover by means of the field effect transistor structure fabricated on the basis of QW we are바카라 조작able바카라 조작by바카라 조작means바카라 조작of simple changing of바카라 조작the바카라 조작gate바카라 조작voltage,바카라 조작firstly,바카라 조작to바카라 조작realize바카라 조작and바카라 조작study바카라 조작transition바카라 조작2D바카라 조작electron바카라 조작metal – 2D semimetal – 2D hole metal and, secondly,바카라 조작2D semimetallic바카라 조작state with any ratio between the densities바카라 조작of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their바카라 조작simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron바카라 조작mobility바카라 조작jump바카라 조작due바카라 조작to바카라 조작hole바카라 조작screening바카라 조작of바카라 조작electron바카라 조작scattering바카라 조작by바카라 조작impurities, 3)바카라 조작anomalous temperature dependence of 2D semimetal resistance because of electron scattering by heavy holes. It is likely this effect is the first clear demonstration of the바카라 조작direct바카라 조작influence바카라 조작of바카라 조작a바카라 조작particle-particle바카라 조작inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion바카라 조작principal.바카라 조작But바카라 조작the바카라 조작most exiting opportunity appearing due to realization of 2D semimetal is to carry out바카라 조작the바카라 조작direct바카라 조작experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one바카라 조작of바카라 조작the바카라 조작greatest바카라 조작20 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 bound바카라 조작state 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 last바카라 조작time바카라 조작there was absent the system in which this transition could be realized and then바카라 조작directly바카라 조작fixed바카라 조작by바카라 조작resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did바카라 조작not바카라 조작fit바카라 조작because바카라 조작of바카라 조작the 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. It바카라 조작is바카라 조작shown바카라 조작that바카라 조작the바카라 조작transition바카라 조작metal – EI바카라 조작is바카라 조작similar바카라 조작to superconductor-normal metal transition and described by BCS (Bardeen-Coopper-Schrieffer)-scenario: up to the critical temperature Tc ≈ 1 K no temperature dependence of the바카라 조작transport바카라 조작and바카라 조작capacitance response of the system is바카라 조작observed바카라 조작but just바카라 조작below바카라 조작this바카라 조작temperature바카라 조작the바카라 조작strong바카라 조작insulator바카라 조작behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,바카라 조작hjlee@postech.ac.kr)
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