TY - JOUR

T1 - Stability of Sarma phases in density imbalanced electron-hole bilayer systems

AU - SubasI, A. L.

AU - Pieri, P.

AU - Senatore, G.

AU - Tanatar, B.

PY - 2010/2/25

Y1 - 2010/2/25

N2 - We study excitonic condensation in an electron-hole bilayer system with unequal layer densities at zero temperature. Using mean-field theory we solve the Bardeen-Cooper-Schrieffer (BCS) gap equations numerically and investigate the effects of intralayer interactions. The electron-hole system evolves from BCS in the weak coupling limit to Bose-Einstein condensation (BEC) in the strong coupling limit. We analyze the stability of the Sarma phase with k,-k pairing by calculating the superfluid mass density and also by checking the compressibility matrix. We find that with bare Coulomb interactions the superfluid density is always positive in the Sarma phase, due to a peculiar momentum structure of the gap function originating from the singular behavior of the Coulomb potential at zero momentum and the presence of a sharp Fermi surface. Introducing a simple model for screening, we find that the superfluid density becomes negative in some regions of the phase diagram, corresponding to an instability toward a Fulde-Ferrel-Larkin-Ovchinnikov-type superfluid phase. Thus, intralayer interaction and screening together can lead to a rich phase diagram in the BCS-BEC crossover regime in electron-hole bilayer systems.

AB - We study excitonic condensation in an electron-hole bilayer system with unequal layer densities at zero temperature. Using mean-field theory we solve the Bardeen-Cooper-Schrieffer (BCS) gap equations numerically and investigate the effects of intralayer interactions. The electron-hole system evolves from BCS in the weak coupling limit to Bose-Einstein condensation (BEC) in the strong coupling limit. We analyze the stability of the Sarma phase with k,-k pairing by calculating the superfluid mass density and also by checking the compressibility matrix. We find that with bare Coulomb interactions the superfluid density is always positive in the Sarma phase, due to a peculiar momentum structure of the gap function originating from the singular behavior of the Coulomb potential at zero momentum and the presence of a sharp Fermi surface. Introducing a simple model for screening, we find that the superfluid density becomes negative in some regions of the phase diagram, corresponding to an instability toward a Fulde-Ferrel-Larkin-Ovchinnikov-type superfluid phase. Thus, intralayer interaction and screening together can lead to a rich phase diagram in the BCS-BEC crossover regime in electron-hole bilayer systems.

UR - http://www.scopus.com/inward/record.url?scp=77954867761&partnerID=8YFLogxK

U2 - 10.1103/PhysRevB.81.075436

DO - 10.1103/PhysRevB.81.075436

M3 - Article

AN - SCOPUS:77954867761

SN - 1098-0121

VL - 81

JO - Physical Review B - Condensed Matter and Materials Physics

JF - Physical Review B - Condensed Matter and Materials Physics

IS - 7

M1 - 075436

ER -