Helical and topological phase detection based on nonlocal conductance measurements in a three terminal junction

TL;DR

This paper introduces a nonlocal conductance measurement method in a three-terminal junction to detect helical states and topological superconducting phases in nanowires, overcoming limitations of traditional two-terminal approaches.

Contribution

It presents a novel approach using nonlocal conductance in a three-terminal setup to reliably identify helical and topological phases, reducing ambiguity from other phenomena.

Findings

Nonlocal conductance is enhanced in the helical gap regime.

The method can detect topological superconducting phases.

Spin-dependent electron trajectories are key to the detection mechanism.

Abstract

The helical state is a fundamental prerequisite for many spintronics applications and Majorana zero mode engineering in nanoscopic semiconductors. Its existence in quasi-one-dimensional nanowires was predicted to be detectable as a characteristic reentrant behavior in the conductance, which in a typical two-terminal architecture may be difficult to distinguish from other possible phenomena such as Fabry-Perot oscillations. Here we present an alternative method of helical gap detection free of the mentioned ambiguity, and based on the nonlocal conductance measurements in a three-terminal junction. We find that the interplay between the spin-orbit coupling and the perpendicular magnetic field leads to a spin-dependent trajectory of electrons and as a consequence a preferential injection of electrons in one of the arms. This causes a remarkable enhancement of nonlocal conductance in the helical gap regime. We show that this phenomenon can be also used to detect the topological superconducting phase when the junction is partially proximitized by an s-wave superconductor.