Monday, July 15, 2013

1307.3505 (Benjamin M. Fregoso et al.)

Electrical detection of topological phase transitions in disordered
Majorana nanowires

Benjamin M. Fregoso, Alejandro M. Lobos, S. Das Sarma
We study a disordered superconducting nanowire, with broken time-reversal and spin-rotational symmetry, which can be driven into a topological phase with end Majorana bound states by an externally applied magnetic field. It is known that, as a function of disorder strength, the Majorana nanowire has a delocalization quantum phase transition transition from a topologically non-trivial phase, which supports Majorana bound states, to a non-topological insulating phase without them. On both sides of the transition, the system has localized wave functions at zero energy albeit with very different topological properties. We propose a simple electrical transport measurement to detect the localization-delocalization transition occurring in the bulk of the nanowire. The basic idea consists of measuring the difference of conductances at one end of the wire obtained at different values of the coupling to the opposite lead. We show that this experiment reveals the non-local correlations between the left and right ends of the nanowire emergent only at the topological transition. Hence, while the proposed experiment does not directly probe the end Majorana bound states, it might provide direct evidence for the bulk topological quantum phase transition itself.
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