Josephson diode and spin-valve effects on the surface of altermagnet CrSb

TL;DR

This study demonstrates Josephson diode and spin-valve effects on CrSb surfaces, revealing the interplay of topological surface states and altermagnetic spin splitting in superconducting junctions.

Contribution

First experimental observation of Josephson diode and spin-valve effects on altermagnet CrSb surfaces, linking topological states with altermagnetic properties.

Findings

Mirrored $dV/dI(B)$ curves indicate Josephson spin valve behavior.

Direct measurement confirms Josephson diode effect in the devices.

Superconducting gap oscillates in magnetic field, resembling FFLO behavior.

Abstract

We experimentally investigate charge transport in In-CrSb and In-CrSb-In proximity devices, which are formed as junctions between superconducting indium leads and thick single crystal flakes of altermagnet CrSb. For double In-CrSb-In junctions, $dV/dI(B)$ curves are mirrored in respect to zero field for two magnetic field sweep directions, which is characteristic behavior of a Josephson spin valve. Also, we demonstrate Josephson diode effect by direct measurement of the critical current for two opposite directions in external magnetic field. We interpret these observations as a joint effect of the spin-polarized topological surface states and the altermagnetic spin splitting of the bulk bands in CrSb. For a single In-CrSb interface, the superconducting gap oscillates in magnetic field for both field orientations, which strongly resembles the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) behavior. FFLO is based on finite-momentum Cooper pairing, therefore, it is fully compatible with the requirements for the Josephson diode effect.