Bistability and discontinuity in the tunnel current of two-dimensional electron-hole layers

We present a detailed study of a recently reported discontinuity and bistability in a 12-nm GaAs/AlAs single-barrier p-i-n heterostructure, where a system of spatially separated two-dimensional electron and hole (e-h) layers of equal and tunable density is realized. Both features appear at T less than or similar to 300 mK and are strongly enhanced in a magnetic field B greater than or similar to 10 T perpendicular to the layers, whereas they are suppressed by B similar to1 T parallel to the layers. They correspond to a discontinuity in the e-h density and in the phase of the current magneto-oscillations. Whereas the high-current state has the expected properties of the uncoupled e-h layers, the low-current state behaves anomalously under all circumstances, and we identify them with a gas of spatially indirect excitons with binding energy 0.03 meV less than or similar toE(b)less than or similar to0.3 meV and 0.5 meV less than or similar toE(b)less than or similar to5 meV at B =0 and B=10 T, respectively. We interpret the bistability as a transition between the two regimes, which arises because of the competition between the in-plane screening, determined by the average e-e (h-h) distance and the magnetic length, and the interlayer e-h attraction. [S0163-1829(00)08143-1].