Altermagnetism and Room-Temperature Metal-to-Insulator Transition in CsCr$_2$S$_2$O

TL;DR

This study reports the discovery of a room-temperature altermagnet and a concurrent metal-insulator transition in CsCr$_2$S$_2$O, linking two key phenomena in a single material with potential spintronic applications.

Contribution

The paper demonstrates the coexistence of altermagnetism and a Verwey-type metal-insulator transition in CsCr$_2$S$_2$O at room temperature, a novel finding in the field.

Findings

CsCr$_2$S$_2$O exhibits room-temperature altermagnetism with C-type antiferromagnetic order.

A metal-insulator transition occurs at 305 K, driven by structural distortion and charge ordering.

First-principles calculations reveal significant spin-split electronic structures in both states.

Abstract

Metal-to-insulator transitions (MITs), particularly near room temperature, have been extensively studied in nonmagnetic and conventional ferromagnetic and antiferromagnetic systems, yet the co-emergence of MIT and altermagnetism (AM) remains unexplored. Here, a layered chromium-based compound CsCr$_2$S$_2$O that realizes this coexistence was synthesized. It crystalizes in CeCr$_2$Si$_2$C-type structure with Cr moments orders in a C-type antiferromagnetic configuration below $T_\mathrm{N}$ = 326 K, constituting a room-temperature d-wave altermagnet. In the altermagnetic state, a subsequent Verwey-type MIT appears at $T_\mathrm{MI}$ = 305 K, driven by a tetragonal-to-orthorhombic structural distortion and stripe charge ordering of Cr$^{+2}$/Cr$^{+3}$ ions, while maintaining its altermagnetic character. First-principles calculations show moment-dependent spin-split electronic structures with maximum splitting energies of ~0.6 eV and ~0.3 eV in the metallic and insulating states, respectively. Our work links the two prominent phenomena, MIT and AM, in a single material, establishing a new platform for potential spintronic applications.