SDW driven "magnetic breakdown" in a d-wave altermagnet KV$_2$Se$_2$O

Altermagnets, combining zero net magnetization with intrinsic spin splitting, demonstrate unique quantum phenomena crucial for spintronic applications. KV$_2$Se$_2$O is proven to be a d-wave altermagnet with phase transition from a checkerboard-type (C-type) antiferromagnetic (AFM) state to a spin density wave (SDW) state as the temperature decreases. After phase transition, the apparent paradox emerges where angle-resolved photoemission spectroscopy (ARPES) reveals negligible Fermi surface modifications, while physical property measurement system (PPMS) measurements uncover substantial changes in transport properties. Our study explores the microscopic mechanisms governing phase-dependent transport properties of KV$_2$Se$_2$O base on first-principles calculations. The spin canting driven by periodic spin modulation in the SDW phase reduces the magnetic symmetry of KV$_2$Se$_2$O. The resultant band degeneracy lifting and Fermi surface reconstruction induce the ``magnetic breakdown" phenomenon, which alters carrier trajectories, modifies carrier concentration, strengthens electron-hole compensation, and ultimately accounts for the contrasting magnetic-field-dependent Hall resistivity relative to the C-type AFM state. Our work proposes an innovative method for identifying the electronic structure evolution across phase transitions from transport signatures, providing a novel paradigm for altermagnets research.

💡 Research Summary

The paper investigates the puzzling discrepancy between the electronic structure and transport properties of the d‑wave altermagnet KV₂Se₂O across its temperature‑driven phase transition from a checkerboard‑type (C‑type) antiferromagnetic (AFM) state to a spin‑density‑wave (SDW) state. Angle‑resolved photoemission spectroscopy (ARPES) shows virtually unchanged Fermi‑surface (FS) topology after the transition, yet physical‑property measurements reveal a dramatic enhancement of Hall resistivity (ρ_yx) and a distinct magnetoresistance (MR) behavior. To resolve this paradox, the authors combine density‑functional theory (DFT) calculations, magnetic space‑group symmetry analysis, and Boltzmann transport simulations.

In the C‑type AFM phase, the magnetic symmetry