Detection of Majorana zero modes bound to Josephson vortices in planar superconductor-topological insulator-superconductor junctions

TL;DR

This paper investigates how Majorana zero modes bound to Josephson vortices in superconductor-topological insulator-superconductor junctions can be detected, analyzing supercurrent signatures and proposing complementary measurement techniques.

Contribution

It provides a detailed analysis of supercurrent signatures of Majorana zero modes and proposes new experimental methods for their detection beyond Fraunhofer patterns.

Findings

Fraunhofer signatures are insufficient for detecting vortex MZMs

Supercurrent measurements can be complemented by STM and microwave spectroscopy

The study offers practical guidance for experimental verification of MZMs

Abstract

We study signatures of Majorana zero modes (MZMs) bound to Josephson vortices in superconductor-three-dimensional topological insulator-superconductor (S-TI-S) Josephson junctions placed in a perpendicular magnetic field. First, using semiclassical analytical as well as numerical techniques, we calculate the spatially resolved supercurrent density carried by the low-energy Caroli-de Gennes-Matricon (CdGM) states in the junction. Motivated by a recent experiment [Yue et al., Phys. Rev. B 109, 094511 (2024)], we discuss if and how the presence of vortex MZMs is reflected in supercurrent measurements, showing that Fraunhofer signatures alone are not suitable to reliably detect vortex MZMs. Next, we propose two ways in which we believe supercurrent measurements could be complemented to further verify that the junction does indeed host MZMs. Explicitly, we discuss how additional Majorana signatures could be obtained by (1) mapping out the local density of states in the junction via scanning tunneling microscopy techniques, and (2) microwave spectroscopy of the spectrum of low-energy CdGM states in the junction.