Locking and unlocking of the counterflow transport in nu=1 quantum Hall bilayers by tilting of magnetic field

Abstract

The counterflow transport in quantum Hall bilayers provided by superfluid excitons is locked at small input currents due to a complete leakage caused by the interlayer tunneling. We show that the counterflow critical current I_c^{CF} above which the system unlocks for the counterflow transport can be controlled by a tilt of magnetic field in the plane perpendicular to the current direction. The effect is asymmetric with respect to the tilting angle. The unlocking is accompanied by switching of the systems from the d.c. to the a.c. Josephson state. Similar switching takes place for the tunneling set-up when the current flowing through the system exceeds the critical value I_c^T. At zero tilt the relation between the tunnel and counterflow critical currents is I_c^T=2 I_c^{CF}. We compare the influence of the in-plane magnetic field component B_\parallel on the critical currents I_c^{CF} and I_c^T. The in-plane magnetic field reduces the tunnel critical current and this reduction is symmetric with respect to the tilting angle. It is shown that the difference between I_c^{CF} and I_c^T is essential at field |B_\parallel|\lesssim \phi_0/d \lambda_J, where \phi_0 is the flux quantum, d is the interlayer distance, and \lambda_J is the Josephson length. At larger B_\parallel the critical currents I_c^{CF} and I_c^T almost coincide each other.Comment: 10 pages, 1 fi