Order formation and superfluidity of excitons in type-II semiconductor quantum wells

T. Iida and M. Tsubota
Phys. Rev. B 60, 5802 – Published 15 August 1999
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Abstract

The condensed state and superfluidity of excitons in type-II semiconductor quantum wells (QW’s) are investigated theoretically. Since the excitons in type-II QW’s have translational motion along the layer, the assembly of them is regarded as an interacting dilute quasi-two-dimensional Bose gas. This system is advantageous for our purpose because those excitons have a long lifetime of the order of 106s, and their transport mechanism can be directly studied in experiments by observing electric current since the excitons consist of spatially separated electron-hole pairs. Using the exciton wave functions obtained by the variational method, the exciton-exciton interaction is calculated and found to be repulsive when the thickness of the QW is thinner than a critical value. To illustrate the situation, we carry out the numerical computation adopting a model system with material constants appropriate to GaAs/AlAs type-II QW’s. The basic equation for the phase of the condensate wave function is derived when the exciton system is irradiated by a weak laser light at zero temperature. Solving the equation in the presence of the external current Jex, we study the stationary spatial pattern of the phase of the condensate wave function. It is shown that there appears a vortex lattice with a net supercurrent when Jex is larger than a critical value; the period of the lattice is determined as a function of Jex. We calculate the magnetic field induced by the current in the vortex lattice, and discuss a possibility of an experimental observation of the critical current. Such a direct observation of the exciton transport will provide unambiguous experimental evidence for the superfluidity of excitons.

  • Received 4 January 1999

DOI:https://doi.org/10.1103/PhysRevB.60.5802

©1999 American Physical Society

Authors & Affiliations

T. Iida and M. Tsubota

  • Department of Physics, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan

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Issue

Vol. 60, Iss. 8 — 15 August 1999

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