New signatures of the spin gap in quantum point contacts

K L Hudson,J Von Delft,J Adam,Q Wang,L A Yeoh,D A Ritchie,O Klochan,O Goulko,A D Wieck,A Ludwig,I Farrer,A Srinivasan,A R Hamilton

doi:10.1038/s41467-020-19895-3

Abstract

One dimensional semiconductor systems with strong spin-orbit interaction are both of fundamental interest and have potential applications to topological quantum computing. Applying a magnetic field can open a spin gap, a pre-requisite for Majorana zero modes. The spin gap is predicted to manifest as a field dependent dip on the first 1D conductance plateau. However, disorder and interaction effects make identifying spin gap signatures challenging. Here we study experimentally and numerically the 1D channel in a series of low disorder p-type GaAs quantum point contacts, where spin-orbit and hole-hole interactions are strong. We demonstrate an alternative signature for probing spin gaps, which is insensitive to disorder, based on the linear and non-linear response to the orientation of the applied magnetic field, and extract a spin-orbit gap ΔE ≈ 500 μeV. This approach could enable one-dimensional hole systems to be developed as a scalable and reproducible platform for topological quantum applications.

Highlights

One dimensional semiconductor systems with strong spin-orbit interaction are both of fundamental interest and have potential applications to topological quantum computing
The physics of 1D electron and hole systems has been an area of ongoing research interest since conductance quantised in integer multiples of 2e2/h was discovered in short quantum point contacts (QPCs) in GaAs heterostructures[1,2]
Figure. 1b–d shows schematically how the conductance of a QPC with a saddle point potential mω2x x2 þ mω2y y2 depends on the applied magnetic field B, the strength of electron–electron interactions U, and spin–orbit interaction R

Summary

Introduction

One dimensional semiconductor systems with strong spin-orbit interaction are both of fundamental interest and have potential applications to topological quantum computing. We demonstrate an alternative signature for probing spin gaps, which is insensitive to disorder, based on the linear and non-linear response to the orientation of the applied magnetic field, and extract a spin-orbit gap ΔE ≈ 500 μeV. This approach could enable one-dimensional hole systems to be developed as a scalable and reproducible platform for topological quantum applications. The system is tuned from the trivial to the topological regime by the application of a magnetic field perpendicular to the effective spin–orbit field BSOI in the wire This mixes the two chiral spin species, opening up a spin gap at k = 0.

Methods

Results

Conclusion