Tunable valley polarization and spin splitting in altermagnetic <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">F</mi><msub><mi mathvariant="normal">e</mi><mn>2</mn></msub><mi>Mo</mi><msub><mi mathvariant="normal">S</mi><mn>2</mn></msub><msub><mi>X</mi><mn>2</mn></msub></mrow><mo>(</mo><mrow><mi>X</mi><mo>=</mo><mi mathvariant="normal">S</mi></mrow><mo>,</mo><mi mathvariant="normal">Se</mi><mo>,</mo><mi mathvariant="normal">Te</mi><mo>)</mo></math> via symmetry engineering

Quan Shen; Wenhu Liao; Hairui Bao; Degao Xu; Jianing Tan; Jiansheng Dong; Gang Ouyang

doi:10.1103/94ll-cldp

Tunable valley polarization and spin splitting in altermagnetic $F e_{2} Mo S_{2} X_{2} (X = S, Se, Te)$ via symmetry engineering

Quan Shen¹, Wenhu Liao ¹, Hairui Bao¹, Degao Xu², Jianing Tan ^1,*, Jiansheng Dong ^1,†, and Gang Ouyang ^3,‡

¹Department of Physics, Jishou University, Jishou 416000, Hunan, China
²School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou 434023, China
³Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education, Key Laboratory for Matter Microstructure and Function of Hunan Province, School of Physics and Electronics, Hunan Normal University, Changsha 410081, China

^*Contact author: jianingtan@hunnu.edu.cn
^†Contact author: jsdong@jsu.edu.cn
^‡Contact author: gangouy@hunnu.edu.cn

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Phys. Rev. Materials 9, 114404 – Published 10 November, 2025

DOI: https://doi.org/10.1103/94ll-cldp

Abstract

The altermagnetic state combines broken time-reversal symmetry with compensated magnetic order to generate spin-split bands at zero net magnetization and offering promising spintronic functionalities. In this work, we use first-principles calculations to demonstrate deterministic control of valley and spin states in two-dimensional altermagnetic $F e_{2} Mo S_{2} X_{2}$ ( $X = S$ , Se, Te). Monolayer $F e_{2} Mo S_{2} S e_{2}$ exhibits giant strain tunable valley polarization (58 meV at 4% tensile), while $A A^{1} - stacked$ bilayer $F e_{2} Mo S_{2} S e_{2}$ show electrically programmable spin splitting (105 meV and 133 meV in X/Y valleys at $E_{z} = 0.1 V / Å$ ). Spin-flip switching, enabled by magnetic moment reversal and detected via magneto-optical Kerr contrast, emerges as a distinct phenomenon in bilayer $F e_{2} Mo S_{2} S e_{2}$ . These findings establish two-dimensional altermagnetic $F e_{2} Mo S_{2} X_{2}$ ( $X = S$ , Se, Te) as a platform for valleytronics, with design principles applicable to ultra-low-power spintronic devices.

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Tunable valley polarization and spin splitting in altermagnetic $F e_{2} Mo S_{2} X_{2} (X = S, Se, Te)$ via symmetry engineering

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Tunable valley polarization and spin splitting in altermagnetic Fe2MoS2X2(X=S,Se,Te) via symmetry engineering

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Tunable valley polarization and spin splitting in altermagnetic $F e_{2} Mo S_{2} X_{2} (X = S, Se, Te)$ via symmetry engineering