Electrical transport measurement of exciton condensate in barrier-separated InAs/GaSb bilayer system

Exciton condensate in semiconductors has been one of the most interesting research fields in condensed matter physics in the last few decades. To extend the exciton lifetime, barrier-separated double quantum wells (QW) are used to prevent the recombination of excitons, where the electrons and holes reside in different QWs separately. The excitons in such nanostructure are so-called real-space indirect excitons. The first observation of real-space indirect exciton condensate is in the barrier-separated GaAs, in which the excitons are excited by light under a strong electric field. However, since the bandgap (E_g) of GaAs is much larger than the binding energy (E_B) of exciton which is usually several meVs, the lifetime of excitons and the condensate is very limited. One way to realize the condensate of the real-space indirect exciton with infinite lifetime is to exert a strong magnetic field to generate landau levels in both QWs. When the magnetic field is strong enough, the electrons (holes) will partially fill the lowest Landau level. Then the electrons and holes at the lowest Landau level will pair together as excitons and condensate at low temperatures. The evidence of such exciton condensate was found both in GaAs double QWs and double-layer graphene systems by electrical transport measurement.

Another way to realize excitons with infinite lifetime is to find a semiconductor system with E_g<E_B. Especially when E_g<0, i.e. in a semiconductor system with an inverted band structure where the electrons and holes can exist simultaneously. InAs/GaSb double QWs is such a system in which the conduction band minimum of InAs is lower than the valance band maximum of GaSb. Here, I will present the electrical transport measurement of exciton condensate in barrier-separated InAs/GaSb including the fabrication of independent contacts on it.