Bistability and discontinuity in the tunnel current of two-dimensional electron-hole layers - art. no. 115307

We present a detailed study of a recently reported discontinuity and bistab ility in a 12-nm GaAs/AlAs single-barrier p-i-n heterostructure, where a sy stem of spatially separated two-dimensional electron and hole (e-h) layers of equal and tunable density is realized. Both features appear at T less th an or similar to 300 mK and are strongly enhanced in a magnetic field B gre ater 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-os cillations. Whereas the high-current state has the expected properties of t he uncoupled e-h layers, the low-current state behaves anomalously under al l circumstances, and we identify them with a gas of spatially indirect exci tons with binding energy 0.03 meV less than or similar toE(b)less than or s imilar to0.3 meV and 0.5 meV less than or similar toE(b)less than or simila r 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 competit ion between the in-plane screening, determined by the average e-e (h-h) dis tance and the magnetic length, and the interlayer e-h attraction. [S0163-18 29(00)08143-1].