2026/07/28 by Pritesh Srivastava, Rahul Verma, Bahadur Singh
Physics and Astronomy · #cond-mat.mtrl-sci
arxiv created 2026/07/30 · arxiv updated 2026/07/31
Crystalline symmetries stabilize topological states with distinct electronic properties, while altermagnets exhibit momentum-dependent spin splitting without net magnetization. Here, we combine first-principles calculations with a minimal tight-binding model to realize C-paired spin-valley-locked nodal-line fermions in the d-wave altermagnet AV2X2O (A = Rb, Cs, or K; X = Te, Se, or S). The low-energy electronic structure hosts coexisting spin-degenerate and spin-polarized nodal lines around C4z-paired valleys near the Fermi level. The spin-polarized nodal lines are protected by the out-of-plane mirror symmetry Mz and remain robust against spin-orbit coupling. The minimal model reveals their microscopic origin and establishes a general design principle for their isolation. Layer engineering and electronic correlations serve as material-specific knobs for realizing these isolated spin-valley-locked nodal lines near the Fermi level. Our results establish the AV2X2O family as a versatile platform for exploring topological spin-valley locking in d-wave altermagnets.