토토 세븐PHYSICS/BK21 SEMINAR[09.08.20]
관련링크
본문
"Two-dimensional semimetaland excitonic insulator
Ø토토 세븐Speaker :토토 세븐 Dr.토토 세븐Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø토토 세븐Place : Physics Seminar Room (Science Bldg, 3-201)
Ø토토 세븐Date & Time :토토 세븐Aug, 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 세븐recently토토 세븐realized for토토 세븐the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in토토 세븐wide토토 세븐(thickness of 18 nm – 21 nm) undoped HgTe QWs with토토 세븐the토토 세븐reduced토토 세븐symmetry토토 세븐surfaces (such as (013)토토 세븐and (112)).토토 세븐Because토토 세븐of토토 세븐an inverted band structure and respectively the peculiar properties of토토 세븐size토토 세븐quantization토토 세븐in토토 세븐these토토 세븐QWs토토 세븐the 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 세븐Moreover by means of the field effect transistor structure fabricated on the basis of QW we are토토 세븐able토토 세븐by토토 세븐means토토 세븐of simple changing of토토 세븐the토토 세븐gate토토 세븐voltage,토토 세븐firstly,토토 세븐to토토 세븐realize토토 세븐and토토 세븐study토토 세븐transition토토 세븐2D토토 세븐electron토토 세븐metal – 2D semimetal – 2D hole metal and, secondly,토토 세븐2D semimetallic토토 세븐state with any ratio between the densities토토 세븐of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their토토 세븐simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron토토 세븐mobility토토 세븐jump토토 세븐due토토 세븐to토토 세븐hole토토 세븐screening토토 세븐of토토 세븐electron토토 세븐scattering토토 세븐by토토 세븐impurities, 3)토토 세븐anomalous 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 세븐direct토토 세븐influence토토 세븐of토토 세븐a토토 세븐particle-particle토토 세븐inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion토토 세븐principal.토토 세븐But토토 세븐the토토 세븐most exiting opportunity appearing due to realization of 2D semimetal is to carry out토토 세븐the토토 세븐direct토토 세븐experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one토토 세븐of토토 세븐the토토 세븐greatest토토 세븐20 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 세븐state 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 세븐time토토 세븐there was absent the system in which this transition could be realized and then토토 세븐directly토토 세븐fixed토토 세븐by토토 세븐resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did토토 세븐not토토 세븐fit토토 세븐because토토 세븐of토토 세븐the 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 세븐is토토 세븐shown토토 세븐that토토 세븐the토토 세븐transition토토 세븐metal – EI토토 세븐is토토 세븐similar토토 세븐to 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 세븐transport토토 세븐and토토 세븐capacitance response of the system is토토 세븐observed토토 세븐but just토토 세븐below토토 세븐this토토 세븐temperature토토 세븐the토토 세븐strong토토 세븐insulator토토 세븐behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,토토 세븐hjlee@postech.ac.kr)
"
Ø토토 세븐Speaker :토토 세븐 Dr.토토 세븐Z. D. Kvon [Institute of Semiconductor Physics, Novosibirsk, Russia]
Ø토토 세븐Place : Physics Seminar Room (Science Bldg, 3-201)
Ø토토 세븐Date & Time :토토 세븐Aug, 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 세븐recently토토 세븐realized for토토 세븐the first time in quantum wells (QWs) on basis of zero gap semiconductor HgTe. It is shown that this 2D semimetal exists in토토 세븐wide토토 세븐(thickness of 18 nm – 21 nm) undoped HgTe QWs with토토 세븐the토토 세븐reduced토토 세븐symmetry토토 세븐surfaces (such as (013)토토 세븐and (112)).토토 세븐Because토토 세븐of토토 세븐an inverted band structure and respectively the peculiar properties of토토 세븐size토토 세븐quantization토토 세븐in토토 세븐these토토 세븐QWs토토 세븐the 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 세븐Moreover by means of the field effect transistor structure fabricated on the basis of QW we are토토 세븐able토토 세븐by토토 세븐means토토 세븐of simple changing of토토 세븐the토토 세븐gate토토 세븐voltage,토토 세븐firstly,토토 세븐to토토 세븐realize토토 세븐and토토 세븐study토토 세븐transition토토 세븐2D토토 세븐electron토토 세븐metal – 2D semimetal – 2D hole metal and, secondly,토토 세븐2D semimetallic토토 세븐state with any ratio between the densities토토 세븐of 2D electrons (Ns) and 2D holes (Ps). So a lot of new interesting properties caused by their토토 세븐simultaneous existence have been observed. These are: 1) sign-variable Hall effect and positive magnetoresistance; 2) electron토토 세븐mobility토토 세븐jump토토 세븐due토토 세븐to토토 세븐hole토토 세븐screening토토 세븐of토토 세븐electron토토 세븐scattering토토 세븐by토토 세븐impurities, 3)토토 세븐anomalous 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 세븐direct토토 세븐influence토토 세븐of토토 세븐a토토 세븐particle-particle토토 세븐inelastic Landau scattering on metal resistance and correspondingly of Pauli exclusion토토 세븐principal.토토 세븐But토토 세븐the토토 세븐most exiting opportunity appearing due to realization of 2D semimetal is to carry out토토 세븐the토토 세븐direct토토 세븐experimental observation of excitonic insulator (EI) state predicted almost fifty years ago by one토토 세븐of토토 세븐the토토 세븐greatest토토 세븐20 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 세븐state 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 세븐time토토 세븐there was absent the system in which this transition could be realized and then토토 세븐directly토토 세븐fixed토토 세븐by토토 세븐resistance measurement. Conventional tree-dimensional semimetal such as Bi or Sb did토토 세븐not토토 세븐fit토토 세븐because토토 세븐of토토 세븐the 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 세븐is토토 세븐shown토토 세븐that토토 세븐the토토 세븐transition토토 세븐metal – EI토토 세븐is토토 세븐similar토토 세븐to 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 세븐transport토토 세븐and토토 세븐capacitance response of the system is토토 세븐observed토토 세븐but just토토 세븐below토토 세븐this토토 세븐temperature토토 세븐the토토 세븐strong토토 세븐insulator토토 세븐behavior characterizing by the gap of about few Kelvins appears.
Contact Person : Prof. Hu-Jong Lee(054-279-2072,토토 세븐hjlee@postech.ac.kr)
"
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