Full tomography of topological Andreev bands in graphene Josephson junctions

TL;DR

This study experimentally maps the topological band structure of three-terminal graphene Josephson junctions, revealing a transition from gapped to gapless states, demonstrating potential for engineering complex topologies in quantum devices.

Contribution

First experimental tomography of topological Andreev bands in graphene Josephson junctions using tunnelling spectroscopy and magnetic flux control.

Findings

Observation of topological transition from gapped to gapless states

Mapping of Andreev bound state spectrum as a function of phase differences

Potential for engineering higher-dimensional topological band structures

Abstract

Multiply connected electronic networks threaded by flux tubes have been proposed as a platform for adiabatic quantum transport and topological states. Multi-terminal Josephson junction (MTJJ) has been suggested as a pathway to realize this concept. Yet, the manifestations of topology in MTJJ remain open for experimental study. Here, we investigated the artificial topological band structure of three-terminal graphene Josephson junctions. Employing tunnelling spectroscopy and magnetic flux gates, we captured the tomography of the Andreev bound state (ABS) energy spectrum as a function of two independent phase differences. This ABS spectrum exhibits the topological transition from gapped to gapless states, akin to the band structure of nodal-line semimetals. Our results show the potential of graphene-based MTJJs for engineering band topologies in higher dimensions.