Altermagnetic Even-Odd Effects in CsV$_2$Te$_2$O Josephson Junctions

TL;DR

This paper explores how layer parity in CsV$_2$Te$_2$O-based Josephson junctions influences spin-polarized supercurrents, revealing an altermagnetic even-odd effect with potential applications in spintronics.

Contribution

It introduces the concept of layer parity controlling supercurrent polarization in altermagnetic materials, demonstrating a novel even-odd effect in Josephson junctions.

Findings

Spin-polarized supercurrents are fully spin-polarized and anisotropic in monolayer junctions.

Odd-layer junctions support supercurrents, even layers cancel them, showing layer parity as a switch.

Vertical junctions exhibit a period-two oscillation in supercurrent based on layer number.

Abstract

The interplay between conventional superconductivity and unconventional magnetism offers an exciting platform for realizing exotic superconducting phenomena. Here, we investigate Josephson effects in planar and vertical junctions based on CsV$_2$Te$_2$O-family materials, which host hidden $d$-wave altermagnetism with G-type antiferromagnetic order. In monolayer-based planar junctions, the quasi-1D, nearly flat, spin-polarized bands of the altermagnet, when coupled to $s$-wave superconductors, produce a \textit{fully} spin-polarized supercurrent with strong directional anisotropy -- a spin-selective Josephson effect. In multilayers, we uncover an \textit{altermagnetic even-odd effect}: spin-polarized supercurrents persist only in odd-layer planar junctions but cancel exactly in even layers. Thus, layer parity acts as a switch for spin-polarized supercurrent. In vertical junctions, odd-layer barriers enhance equal-spin triplet transport while even layers favor opposite-spin transport, yielding a robust period-two oscillation in the total supercurrent with layer number. These layer-parity-dependent responses represent a general even-odd effect in hidden altermagnets, applicable to diverse magnetic and transport phenomena.