Critical tunneling currents in the regime of bilayer excitons

Lars Tiemann

Max-Planck Institute for Solid State Research, Germany

Coulomb interactions between two closely spaced two-dimensional electron systems (2DES) under strong perpendicular magnetic fields can produce a new quantum Hall state when the filling factor of both 2DES is close to 1/2. This "total filling factor 1" state is believed to be the long-sought Bose condensate of excitons in semiconductors, where an electron from layer 1 is correlated to a vacant state (hole) in layer 2 and vice versa. Interlayer tunneling experiments at total filling factor 1 have shown an I/V characteristic that has an astonishing resemblance to the one of the Josephson effect of superconductivity [1].
However, despite several similarities between the common superconductivity/superfluidity and the total filling factor 1 state, a critical behavior had not be observed so far. Our DC interlayer tunneling experiments in this regime have found evidence for the existence of critical currents I* [2]. Below I*, the four-terminal interlayer resistance is very small but abruptly increases by many orders of magnitude once I>I*. The nearly vanishing 4-terminal interlayer resistance is most likely the direct consequence of the interlayer phase-coherence associated with the Bose condensation. It changes the tunneling electrons into quasiparticles which then can be easily transferred between the layers.
[1] Spielman I B et al., Phys. Rev. Lett. 87, 036803 (2001)
[2] Tiemann L et al., arXiv:0803.2794 (to appear in New Journal of Physics)