Hybridization of sub-gap states in one-dimensional superconductor/semiconductor Coulomb islands

TL;DR

This study investigates one-dimensional superconductor-semiconductor Coulomb islands, revealing how sub-gap states and Majorana modes influence transport properties, with implications for topological quantum computing.

Contribution

It demonstrates the experimental observation of overlapping Majorana zero modes in finite wires through Coulomb blockade measurements and magnetic field effects.

Findings

Coulomb blockade shows Cooper-pair transport without sub-gap states.

Sub-gap states cause oscillations in Coulomb peak positions and heights.

Evidence of Rashba spin-orbit coupling and Majorana mode overlap.

Abstract

We present measurements of one-dimensional superconductor-semiconductor Coulomb islands, fabricated by gate confinement of a two-dimensional InAs heterostructure with an epitaxial Al layer. When tuned via electrostatic side gates to regimes without sub-gap states, Coulomb blockade reveals Cooper-pair mediated transport. When sub-gap states are present, Coulomb peak positions and heights oscillate in a correlated way with magnetic field and gate voltage, as predicted theoretically, with (anti) crossings in (parallel) transverse magnetic field indicating Rashba-type spin-orbit coupling. Overall results are consistent with a picture of overlapping Majorana zero modes in finite wires.