The electronic structures, magnetic transition and Fermi surface instability of room-temperature altermagnet KV$_{2}$Se$_{2}$O

TL;DR

This paper theoretically investigates KV$_2$Se$_2$O, revealing high-temperature altermagnetism, a Lifshitz transition, and Fermi surface nesting that induce a spin-density wave, positioning it as a platform for studying complex quantum phenomena.

Contribution

It confirms the presence of room-temperature altermagnetism in KV$_2$Se$_2$O and uncovers its electronic transitions and Fermi surface instabilities, advancing understanding of altermagnetic materials.

Findings

High-temperature metallic altermagnetism confirmed in KV$_2$Se$_2$O

Lifshitz transition causes metal-insulator-metal transition

Fermi surface nesting induces spin-density wave state

Abstract

Altermagnetism has recently emerged as a distinct and fundamental class of magnetic order. Exploring its interplay with quantum phenomena such as unconventional superconductivity, density-wave instabilities, and many-body effects represents a compelling frontier. In this work, we theoretically confirm the presence of high-temperature metallic altermagnetism in KV$_2$Se$_2$O. We demonstrate that the anomalous metal-insulator-metal transition arises from a Lifshitz transition associated with Fermi surface reconstruction. The previously reported spin-density wave gap is found to lie below the Fermi level in our study and is now recognized to be attributed to the V-shaped density of states, originating from orbital-selective and sublattice-resolved half-metal-like behavior on a specific V atom. Furthermore, we identify the instability from the nesting of spin-momentum-locked two-dimensional Fermi surfaces, which induces the SDW state. These findings position KV$_2$Se$_2$O as a promising platform for investigating the interplay among altermagnetism, unconventional superconductivity, and density-wave order.