Browsing by Author "Su, Jung-Jung"

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Ferminoic Physics in Dipolariton Condensates
(2014-03-17)
Su, Jung-Jung
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Kim, Na Young
;
Yamamoto, Yoshihisa
;
MacDonald, Allan H.
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電子物理學系
An exciton polariton is an extremely light bosonic quasiparticle that is composed of an exciton and a photon. We report on a theoretical study of exciton-polariton condensation in a system with tunnel-coupled quantum wells. Because their excitons can carry an electric dipole moment, these systems have been referred to as dipolariton condensates. We use a fermionic mean-field theory that can address quantum well and other internal exciton degrees of freedom to describe the new physics present in dipolariton condensates. We find that the role of underlying fermonic degrees of freedom is enhanced and predict that metallic condensates can occur at high carrier densities.
Fractional Solitons in Excitonic Josephson Junctions
(2015-10-29)
Hsu, Ya-Fen
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Su, Jung-Jung
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電子物理學系
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Department of Electrophysics
The Josephson effect is especially appealing to physicists because it reveals macroscopically the quantum order and phase. In excitonic bilayers the effect is even subtler due to the counterflow of supercurrent as well as the tunneling between layers (interlayer tunneling). Here we study, in a quantum Hall bilayer, the excitonic Josephson junction: a conjunct of two exciton condensates with a relative phase phi(0) applied. The system is mapped into a pseudospin ferromagnet then described numerically by the Landau-Lifshitz-Gilbert equation. In the presence of interlayer tunneling, we identify a family of fractional sine-Gordon solitons which resemble the static fractional Josephson vortices in the extended superconducting Josephson junctions. Each fractional soliton carries a topological charge Q that is not necessarily a half/full integer but can vary continuously. The calculated current-phase relation (CPR) shows that solitons with Q = phi(0)/2 pi is the lowest energy state starting from zero phi(0) - until phi(0) > pi - then the alternative group of solitons with Q = phi(0)/2 pi - 1 takes place and switches the polarity of CPR.
Fractional Solitons in Excitonic Josephson Junctions (vol 5, 15796, 2015)
(2017-06-07)
Hsu, Ya-Fen
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Su, Jung-Jung
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電子物理學系
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Department of Electrophysics
Microscopic theory of equilibrium polariton condensates
(2016-12-02)
Xue, Fei
;
Wu, Fengcheng
;
Xie, Ming
;
Su, Jung-Jung
;
MacDonald, A. H.
We present a microscopic theory of the equilibrium polariton condensate state of a semiconductor quantum well in a planar optical cavity. The theory accounts for the adjustment of matter excitations to the presence of a coherent photon field, predicts effective polariton-polariton interaction strengths that are weaker and condensate exciton fractions that are smaller than in the commonly employed exciton-photon model, and yields effective Rabi coupling strengths that depend on the detuning of the cavity-photon energy relative to the bare exciton energy. The dressed quasiparticle bands that appear naturally in the theory provide a mechanism for electrical manipulation of polariton condensates.
Plastic response of dislocation glide in solid helium under dc strain-rate loading
(2013-07-24)
Zhou, Caizhi
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Su, Jung-Jung
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Graf, Matthias J.
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Reichhardt, Charles
;
Balatsky, Alexander V.
We develop a model for the gliding of dislocations and plasticity in solid He-4. This model takes into account the Peierls barrier, multiplication and interaction of dislocations, as well as classical thermally and mechanically activated processes leading to dislocation glide. We specifically examine the dc stress-strain curve and how it is affected by temperature, strain rate, and dislocation density. As a function of temperature and shear strain, we observe plastic deformation and discuss how this may be related to the experimental observation of elastic anomalies in solid hcp He-4 that have been discussed in connection with the possibility of supersolidity or giant plasticity. Our theory gives several predictions for the dc stress strain curves, for example, the yield point and the change in the work-hardening rate and plastic dissipation peak, that can be compared directly to constant strain-rate experiments and thus provide bounds on model parameters.
Single interface effects dominate in exciton-condensate/normal-barrier/exciton-condensate (EC/N/EC) structures of long-barrier
(2018-08-02)
Hsu, Ya-Fen
;
Su, Jung-Jung
;
電子物理學系
;
Department of Electrophysics
We study theoretically the exciton-condensate/normal-barrier/exciton-condensate (EC/N/EC) structures in bilayers with a tunable relative phase ?(0) between the two exciton condensates (ECs). It is a setup inspired initially by the superconducting Josephson junction but with a special ingredient added for bilayer systems, namely, the interlayer tunneling. Our results shows that in a EC/N/EC structure of long-barrier, the single Andreev reflection at one EC/N interface dominates-as opposed to the same structure of short-barrier, in which multiple Andreev reflections can be accommodated (similar to the superconducting Josephson junctions). The single interface effect turns the other EC inert and the system can no longer be understood as a Josephson junction. The supercurrent, however, still occurs at the N/EC interface since the current conservation is still fulfilled with the assistance of the interlayer tunneling in barriers. This exotic mechanism gives rise to only a half portion from a fractional soliton of a doubled topological charge 2Q = ?(0)/pi (for the same relative phase ?(0)), as opposed to a full portion fraction soliton of charge Q = ?(0)/2 pi in the structures of short-barriers. We predict the current phase relation for the EC/N/EC structures of long-barriers which can be tested experimentally.
Spatially indirect exciton condensate phases in double bilayer graphene
(2017-01-18)
Su, Jung-Jung
;
MacDonald, Allan H.
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電子物理學系
;
Department of Electrophysics
We present a theory of spatially indirect exciton condensate states in systems composed of a pair of electrically isolated Bernal graphene bilayers. The ground-state phase diagram in a two-dimensional displacement-field/interbilayer-bias space includes layer-polarized semiconductors, spin-density-wave states, exciton condensates, and states with mixed excitonic and spin order. We find that two different condensate states, distinguished by a chirality index, are stable under different electrical control conditions.