Bose-Einstein Condensation of Excitons

Abstract

This note discusses the question as to whether quasi-particles, such as excitons, i.e. , nonlocalized excited states of solids, can ful611 necessary conditions for a Bose-Einstein condensation, and whether such condensation can be observed. Although uncertainties of present data on excitons preclude precise numerical predictions, it is concluded that under certain experimentally attainable circumstances excitons fulfill the necessary conditions, i.e. , condensation is possible. Ways of detecting the condensation are considered, and a specihc experiment is proposed.

Coulomb drag

“…Originally envisioned for optically generated excitons in bulk semiconductors (Blatt et al, 1962;Keldysh and Kopaev, 1964;Keldysh and Kozlov, 1968;Moskalenko, 1962), the phenomenon has been predicted also for indirect excitons in double-layer systems (Lozovik and Yudson, 1976;Shevchenko, 1976).…”

How to make a bilayer exciton condensate flow

“…In their pioneering work on exciton Bose condensation Blatt et al [3] argued that because an exciton is neutral, condensation can not lead to spectacular electrical effects. Experimental studies of quantum Hall exciton condensates have already made it clear [10,14] that this pessimistic conclusion is not valid.…”

“…Electron-hole pair (exciton) condensation has maintained special interest because it has been difficult to realize experimentally, and because exciton phase coherence is never[1] perfectly spontaneous. Although ideal condensates can support[2] an exciton supercurrent, it has not been clear [3] how such a current could be induced or detected, or how its experimental manifestation would be altered by the phase-fixing exciton creation and annihilation processes which are inevitably present. In this article we explain how to induce an exciton supercurrent in separately contacted bilayer condensates, and predict electrical effects which enable unambiguous detection.…”

“…Exciton condensation has so far been realized [10] only in the quantum Hall regime in which band dispersion is irrelevant allowing spontaneous coherence to occur between spatially separated conduction bands, or spatially separated valence bands, under circumstances that are achieved routinely. The considerations explained in this article apply to quantum Hall exciton condensates in the Corbino geometry [11,12], in which current flows across the 2DES bulk, but not directly to the Hall bar geometry [13] in which currents flows along the 2DES edge.In their pioneering work on exciton Bose condensation Blatt et al [3] argued that because an exciton is neutral, condensation can not lead to spectacular electrical effects. Experimental studies of quantum Hall exciton condensates have already made it clear [10,14] that this pessimistic conclusion is not valid.…”

Manifestation of unconventional biexciton states in quantum dots

“…Their condensation into one macroscopic wave function 1,2 , however, is hampered by a couple of obstaclesto mention two of them, the fermionic substructure impairing the transition temperature 3,4 and the frequently fast radiative decay 5,6 . The latter can be cured by a spatial separation of the electron and hole subsystem, either using two coupled quantum wells with a superposed electric field 7,8 or by a single quantum well with a strong inherent electric field induced by the piezoand/or pyroelectricity of the crystal lattice [9][10][11][12] .…”