Physical properties and first-principles calculations of an altermagnet candidate Cs$_{1-\delta}$V$_2$Te$_2$O

TL;DR

This study investigates the crystal structure, magnetic properties, and electronic behavior of Cs$_{1-eta}$V$_2$Te$_2$O, revealing antiferromagnetism, potential Lifshitz transition, and orbital-spin polarization, highlighting its altermagnetic characteristics.

Contribution

It provides the first comprehensive analysis combining experimental and first-principles calculations of an altermagnet candidate Cs$_{1-eta}$V$_2$Te$_2$O, demonstrating its magnetic and electronic properties.

Findings

Antiferromagnetic transition at 293 K confirmed.

Secondary transition near 70 K possibly linked to Lifshitz transition.

V-$d_{yz}/d_{xz}$ electrons are fully orbital- and spin-polarized.

Abstract

We report the crystal growth, structure, physical properties, and first-principles calculations of a vanadium-based oxytelluride Cs$_{1-\delta}$V$_2$Te$_2$O. The material possesses two-dimensional V$_2$O square nets sandwiched by tellurium layers, with local crystallographic symmetry satisfying the spin symmetry for a $d$-wave altermagnet. An antiferromagnetic transition at 293 K is unambiguously evidenced from the measurements of magnetic susceptibility and specific heat. In addition, a secondary transition at $\sim$70 K is also observed, possibly associated with a Lifshitz transition. The first-principles calculations indicate robust N\'{e}el-type collinear antiferromagnetism in the V$_2$O plane. Consequently, spin splittings show up in momentum space, in relation with the real-space mirror/rotation symmetry. Interestingly, the V-$d_{yz}/d_{xz}$ electrons, which primarily contribute the quasi-one-dimensional Fermi surface, turns out to be fully orbital- and spin-polarized, akin to the case of a half metal. Our work lays a solid foundation on the potential applications utilizing altermagnetic properties in vanadium-based oxychalcogenides.