Coupled Spin-Density-Wave and Bond-Order Driven Metal-Insulator Transition in Altermagnetic CsCr$_2$S$_2$O

Chenchao Xu; Wansheng Bai; Guo-Xiang Zhi; Yi Liu; Xiaoqun Wang; Jianhui Dai; Chao Cao

Coupled Spin-Density-Wave and Bond-Order Driven Metal-Insulator Transition in Altermagnetic CsCr$_2$S$_2$O

Strongly Correlated Electrons 2026-07-30 v1

Authors: Chenchao Xu , Wansheng Bai , Guo-Xiang Zhi , Yi Liu , Xiaoqun Wang , Jianhui Dai , Chao Cao

Abstract

A metal-insulator transition (MIT) driven by bond order (BO) coupled with a secondary spin-density wave (SDW) is identified in CsCr $_2$ S $_2$ O. Such coupling is enabled as a result of the broken time-reversal symmetry due to the pre-existing C-type antiferromagnetic (C-AFM) order. First-principles calculations reveal an orbital-selective physics that Cr- $d_{yz}$ orbitals form local moments and establish the altermagnetic order, while the Cr- $d_{xz}$ orbitals remain metallic and hybridize with S- $p_z$ . Thus the low-energy physics is governed by the Cr- $d_{xz}$ and S- $p_z$ orbitals. On-site interactions then enhance a secondary SDW ( $s$ SDW) instability of the itinerant $d_{xz}$ electrons, which couples to the Cr- $d_{xz}$ -S- $p_z$ bonding order. The resulting coupled $s$ SDW-BO simultaneously produces experimentally observed structural distortion, charge disproportionation, local Cr-moment modulation, and gap opening. Our results establish an orbital-selective mechanism upon which pre-existing altermagnetism and electronic correlations cooperate to drive a structural MIT.

Keywords

metal-insulator transition bond order spin-density wave altermagnetism orbital-selective

Cite

@article{arxiv.2607.28329,
  title  = {Coupled Spin-Density-Wave and Bond-Order Driven Metal-Insulator Transition in Altermagnetic CsCr$_2$S$_2$O},
  author = {Chenchao Xu and Wansheng Bai and Guo-Xiang Zhi and Yi Liu and Xiaoqun Wang and Jianhui Dai and Chao Cao},
  journal= {arXiv preprint arXiv:2607.28329},
  year   = {2026}
}