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 IcCF 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 IcT. At zero tilt the relation between the tunnel and counterflow critical currents is IcT=2 IcCF. We compare the influence of the in-plane magnetic field component B on the critical currents IcCF and IcT. 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 IcCF and IcT is essential at field |B| φ0/d λJ, where φ0 is the flux quantum, d is the interlayer distance, and λJ is the Josephson length. At larger B the critical currents IcCF and IcT almost coincide each other.
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