Quantum interference of edge supercurrents in a two-dimensional topological insulator

TL;DR

This paper develops a microscopic theory for magnetic oscillations in supercurrents of 2D topological insulator Josephson junctions, revealing temperature-dependent interference patterns and the influence of protected Andreev bound states.

Contribution

It introduces a detailed microscopic model that explains complex interference phenomena in TI Josephson junctions beyond standard SQUID theory, including temperature effects and Doppler-like current modifications.

Findings

Long junctions show a crossover from SQUID-like to quasiperiodic interference patterns with temperature.

Short junctions exhibit interference mainly at zero magnetic field.

Protected Andreev bound states are responsible for the observed patterns.

Abstract

Josephson weak links made of two-dimensional topological insulators (TIs) exhibit magnetic oscillations of the supercurrent that are reminiscent of those in superconducting quantum interference devices (SQUIDs). We propose a microscopic theory of this effect that goes beyond the approaches based on the standard SQUID theory. For long junctions we find a temperature-driven crossover from Phi_0-periodic SQUID-like oscillations to a 2 Phi_0-quasiperiodic interference pattern with different peaks at even and odd values of the magnetic flux quantum Phi_0=ch/2e. This behavior is absent in short junctions where the main interference signal occurs at zero magnetic field. Both types of interference patterns reveal gapless (protected) Andreev bound states. We show, however, that the usual sawtooth current-flux relationship is profoundly modified by a Doppler-like effect of the shielding current which has been overlooked previously. Our findings may explain recently observed even-odd interference patterns in InAs/GaSb-based TI Josephson junctions and uncover unexplored operation regimes of nano-SQUIDs.