Quantum point contact as a probe of a topological superconductor

TL;DR

This paper demonstrates that conductance plateaus in a ballistic point contact can serve as a clear indicator of a topological superconductor phase, with quantized signatures that are robust against disorder and thermal effects.

Contribution

It introduces a method to identify topological phases in superconductors using ballistic point contact conductance measurements, highlighting advantages over tunnel contacts.

Findings

Conductance shows half-integer plateaus in topologically nontrivial phase.

Disorder destroys higher plateaus but preserves the first quantized plateau.

Ballistic contacts are more robust probes than tunnel contacts.

Abstract

We calculate the conductance of a ballistic point contact to a superconducting wire, produced by the s-wave proximity effect in a semiconductor with spin-orbit coupling in a parallel magnetic field. The conductance G as a function of contact width or Fermi energy shows plateaus at half-integer multiples of 4e^2/h if the superconductor is in a topologically nontrivial phase. In contrast, the plateaus are at the usual integer multiples in the topologically trivial phase. Disorder destroys all plateaus except the first, which remains precisely quantized, consistent with previous results for a tunnel contact. The advantage of a ballistic contact over a tunnel contact as a probe of the topological phase is the strongly reduced sensitivity to finite voltage or temperature.