Symmetry-Related Higher-Order Phonon Anharmonicity in the 2D Altermagnetic Semiconductor V2Se2O

Abstract Altermagnets (AM) enable spin-split electronic structures without strong spin–orbit coupling (SOC), providing a clean platform for investigating intrinsic lattice anharmonicity in spintronic materials. Monolayer V2Se2O exhibits pronounced nonrelativistic spin splitting, while its band structure remains nearly unchanged after including SOC. Its magnetic anisotropy energy is only −0.043 meV per V atom, yet the predicted Néel temperature reaches 432 K, indicating robust room-temperature altermagnetic order. Thermal transport calculations reveal strong higher-order phonon anharmonicity. Its lattice thermal conductivity decreases from 127.00 W/mK with three-phonon scattering to 54.85 W/mK after including four-phonon processes, yet remains higher than that of most magnetic semiconductors. Mode-resolved potential-energy analysis shows that the strong fourth-order anharmonicity is direction-selective and mainly originates from the V–O–V bonding network along the staggered arrangement of magnetic V atoms. These findings establish the symmetry-related origin of higher-order phonon anharmonicity in V2Se2O and highlight its importance for thermal transport in two-dimensional altermagnetic semiconductors.