토토 승무패PHYSICS/BK21 SEMINAR[09.08.20]
관련링크
본문
"Two-dimensional semimetaland excitonic insulator
Ø토토 승무패Speaker :토토 승무패 Dr.토토 승무패Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø토토 승무패Place : Physics Seminar Room (Science Bldg, 3-201)
Ø토토 승무패Date & Time :토토 승무패Aug, 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,토토 승무패recently토토 승무패realized for토토 승무패the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in토토 승무패wide토토 승무패(thickness of 18 nm – 21 nm) undoped HgTe QWs with토토 승무패the토토 승무패reduced토토 승무패symmetry토토 승무패surfaces (such as (013)토토 승무패and (112)).토토 승무패Because토토 승무패of토토 승무패an inverted band structure and respectively the peculiar properties of토토 승무패size토토 승무패quantization토토 승무패in토토 승무패these토토 승무패QWs토토 승무패the 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.토토 승무패Moreover by means of the field effect transistor structure fabricated on the basis of QW we are토토 승무패able토토 승무패by토토 승무패means토토 승무패of simple changing of토토 승무패the토토 승무패gate토토 승무패voltage,토토 승무패firstly,토토 승무패to토토 승무패realize토토 승무패and토토 승무패study토토 승무패transition토토 승무패2D토토 승무패electron토토 승무패metal – 2D semimetal – 2D hole metal and, secondly,토토 승무패2D semimetallic토토 승무패state with any ratio between the densities토토 승무패of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their토토 승무패simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron토토 승무패mobility토토 승무패jump토토 승무패due토토 승무패to토토 승무패hole토토 승무패screening토토 승무패of토토 승무패electron토토 승무패scattering토토 승무패by토토 승무패impurities, 3)토토 승무패anomalous temperature dependence of 2D semimetal resistance because of electron scattering by heavy holes. It is likely this effect is the first clear demonstration of the토토 승무패direct토토 승무패influence토토 승무패of토토 승무패a토토 승무패particle-particle토토 승무패inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion토토 승무패principal.토토 승무패But토토 승무패the토토 승무패most exiting opportunity appearing due to realization of 2D semimetal is to carry out토토 승무패the토토 승무패direct토토 승무패experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one토토 승무패of토토 승무패the토토 승무패greatest토토 승무패20 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 bound토토 승무패state 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 last토토 승무패time토토 승무패there was absent the system in which this transition could be realized and then토토 승무패directly토토 승무패fixed토토 승무패by토토 승무패resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did토토 승무패not토토 승무패fit토토 승무패because토토 승무패of토토 승무패the 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. It토토 승무패is토토 승무패shown토토 승무패that토토 승무패the토토 승무패transition토토 승무패metal – EI토토 승무패is토토 승무패similar토토 승무패to superconductor-normal metal transition and described by BCS (Bardeen-Coopper-Schrieffer)-scenario: up to the critical temperature Tc ≈ 1 K no temperature dependence of the토토 승무패transport토토 승무패and토토 승무패capacitance response of the system is토토 승무패observed토토 승무패but just토토 승무패below토토 승무패this토토 승무패temperature토토 승무패the토토 승무패strong토토 승무패insulator토토 승무패behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,토토 승무패hjlee@postech.ac.kr)
"
Ø토토 승무패Speaker :토토 승무패 Dr.토토 승무패Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø토토 승무패Place : Physics Seminar Room (Science Bldg, 3-201)
Ø토토 승무패Date & Time :토토 승무패Aug, 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,토토 승무패recently토토 승무패realized for토토 승무패the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in토토 승무패wide토토 승무패(thickness of 18 nm – 21 nm) undoped HgTe QWs with토토 승무패the토토 승무패reduced토토 승무패symmetry토토 승무패surfaces (such as (013)토토 승무패and (112)).토토 승무패Because토토 승무패of토토 승무패an inverted band structure and respectively the peculiar properties of토토 승무패size토토 승무패quantization토토 승무패in토토 승무패these토토 승무패QWs토토 승무패the 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.토토 승무패Moreover by means of the field effect transistor structure fabricated on the basis of QW we are토토 승무패able토토 승무패by토토 승무패means토토 승무패of simple changing of토토 승무패the토토 승무패gate토토 승무패voltage,토토 승무패firstly,토토 승무패to토토 승무패realize토토 승무패and토토 승무패study토토 승무패transition토토 승무패2D토토 승무패electron토토 승무패metal – 2D semimetal – 2D hole metal and, secondly,토토 승무패2D semimetallic토토 승무패state with any ratio between the densities토토 승무패of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their토토 승무패simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron토토 승무패mobility토토 승무패jump토토 승무패due토토 승무패to토토 승무패hole토토 승무패screening토토 승무패of토토 승무패electron토토 승무패scattering토토 승무패by토토 승무패impurities, 3)토토 승무패anomalous temperature dependence of 2D semimetal resistance because of electron scattering by heavy holes. It is likely this effect is the first clear demonstration of the토토 승무패direct토토 승무패influence토토 승무패of토토 승무패a토토 승무패particle-particle토토 승무패inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion토토 승무패principal.토토 승무패But토토 승무패the토토 승무패most exiting opportunity appearing due to realization of 2D semimetal is to carry out토토 승무패the토토 승무패direct토토 승무패experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one토토 승무패of토토 승무패the토토 승무패greatest토토 승무패20 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 bound토토 승무패state 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 last토토 승무패time토토 승무패there was absent the system in which this transition could be realized and then토토 승무패directly토토 승무패fixed토토 승무패by토토 승무패resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did토토 승무패not토토 승무패fit토토 승무패because토토 승무패of토토 승무패the 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. It토토 승무패is토토 승무패shown토토 승무패that토토 승무패the토토 승무패transition토토 승무패metal – EI토토 승무패is토토 승무패similar토토 승무패to superconductor-normal metal transition and described by BCS (Bardeen-Coopper-Schrieffer)-scenario: up to the critical temperature Tc ≈ 1 K no temperature dependence of the토토 승무패transport토토 승무패and토토 승무패capacitance response of the system is토토 승무패observed토토 승무패but just토토 승무패below토토 승무패this토토 승무패temperature토토 승무패the토토 승무패strong토토 승무패insulator토토 승무패behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,토토 승무패hjlee@postech.ac.kr)
"
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