Andreev Reflection in Fermi Arc Surface States of Weyl Semimetals

TL;DR

This paper investigates Andreev reflection in Weyl semimetals with Fermi arc surface states, revealing orientation-dependent conductance features and magnetic field effects that serve as signatures for Fermi arc detection.

Contribution

It demonstrates how the orientation of a planar junction influences Andreev reflection in Weyl semimetals, providing a new method to identify Fermi arcs via conductance measurements.

Findings

Orientation-dependent crossover in Andreev reflection

Magnetic field facilitates switching between regimes

Distinct conductance spectra signatures

Abstract

Fermi arc surface states are the hallmark of Weyl semimetals, whose identification is usually challenged by their coexistence with gapless bulk states. Surface transport measurements by fabricating setups on the sample boundary provide a natural solution to this problem. Here, we study the Andreev reflection (AR) in a planar normal metal-superconductor junction on the Weyl semimetal surface with a pair of Fermi arcs. For a conserved transverse momentum, the occurrence of normal reflection depends on the relative orientation between the Fermi arcs and the normal of the junction, which is a direct result of the disconnected Fermi arcs. Consequently, a crossover from the suppressed to perfect AR occurs with varying the orientation of the planar junction, giving rise to a change from double-peak to plateau structure in conductance spectra. Moreover, such a crossover can be facilitated by imposing a magnetic field, making electrons slide along the Fermi arcs so as to switch between two regimes of the AR. Our results provide a decisive signature for the detection of Fermi arcs and open the possibilities of exploring novel phenomenology through their interplay with superconductivity.