Superfluidity of a dilute gas of electron-hole pairs in a bilayer system

The stability conditions for a superfluid phase in double layer systems with pairing of spatially separated electrons and holes were studied in the low density limit, and the general expression for the collective excitation spectrum was obtained. It was shown that as the distance d between the layers increases, a minimum appears in the excitation spectrum. When d reaches a critical value, the superfluid state becomes unstable with respect to the formation of a phase of the Wigner-crystal type. The same instability occurs at a fixed d upon an increase in the density of charge carriers. It was established that the critical distance and the critical density are related through inverse-power dependence. The impact of impurities on the temperature of the superfluid transition was investigated and the conditions under which it is small were established. It was shown that the critical temperature T-c approximate to 100K can be reached in the diluted systems. Published by AIP Publishing.