Tunneling in two-layer systems with electron-hole pairing(Review Article)
National Science Center, Kharkov Institute of Physics and Technology 1 Akademicheskaya Str., Kharkiv 61108, Ukraine
V.N. Karazin Kharkiv National University, 4 Svobody Square, Kharkiv 61022, Ukraine
Received December 3, 2019, published online March 24, 2020
In two-layer n-p systems, a phase-coherent state of electron-hole pairs can arise, generated by the Coulomb attraction of electrons of the n layer to holes from the p layer. In contrast to Josephson junctions, the phase of the order parameter in n–p bilayers is fixed by matrix elements of the interlayer tunneling T12. The phase fixation determines the response of the electron–hole condensate to the electric voltage between the layers, namely: the phase is constant at low voltages, V < Vc, and monotonically in-creases with time at V > Vc. A change in the dynamics of the system at V = Vc leads to a peak in the differential tunneling conductivity. The peak width Vc is proportional to the modulus of the tunnel matrix element |T12|, and its height does not depend on |T12|. Thus, for small |T12| peak is high and narrow. In the case of large two-layer systems, a magnetic field parallel to the layers significantly reduces the peak height. In small two-layer systems, the dependence of the height of the tunneling conduction peak on a parallel magnetic field has a form similar to the Fraunhofer diffraction pattern. The peak of the interlayer differential tunneling conductivity is also strongly suppressed by temperature due to thermal fluctuations of the interlayer voltage.
Key words: two-layer systems, electron-hole pairing, tunneling conductivity.