Altermagnets, combining zero net magnetization with intrinsic spin splitting, demonstrate unique quantum phenomena crucial for spintronic applications. KV2Se2O 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 KV2Se2O base on first-principles calculations. The spin canting driven by periodic spin modulation in the SDW phase reduces the magnetic symmetry of KV2Se2O. 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.
@article{arxiv.2505.00074,
title = {SDW driven "magnetic breakdown" in a d-wave altermagnet KV$_2$Se$_2$O},
author = {Xu Yan and Ziyin Song and Juntao Song and Zhong Fang and Hongming Weng and Quansheng Wu},
journal= {arXiv preprint arXiv:2505.00074},
year = {2026}
}