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<p>In monolayer transition metal dichalcogenides, time-reversal symmetry—combined with broken space-inversion symmetry—defines the spin–valley degree of freedom. As such, the engineering and control of time-reversal symmetry by optical or magnetic fields constitutes the foundation of valleytronics. Here we propose a new approach for the detection of broken time-reversal symmetry and valley imbalance in monolayer WSe<sub>2</sub> based on second-harmonic generation. At room temperature, our method can selectively probe a net valley imbalance generated by ultrafast, coherent and valley-exclusive optical Stark and Bloch–Siegert effects. This work demonstrates the potential and unique capabilities of nonlinear optics as a probe of broken time-reversal symmetry as well as a tool for ultrafast and non-destructive valleytronic operations.</p>

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Nonlinear valley selection rules and all-optical probe of broken time-reversal symmetry in monolayer WSe2

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年1月7日

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  • Paul Herrmann,
  • Sebastian Klimmer,
  • Thomas Lettau,
  • Till Weickhardt,
  • Anastasios Papavasileiou,
  • Kseniia Mosina,
  • Zdeněk Sofer,
  • Ioannis Paradisanos,
  • Daniil Kartashov,
  • Jan Wilhelm,
  • Giancarlo Soavi

摘要

In monolayer transition metal dichalcogenides, time-reversal symmetry—combined with broken space-inversion symmetry—defines the spin–valley degree of freedom. As such, the engineering and control of time-reversal symmetry by optical or magnetic fields constitutes the foundation of valleytronics. Here we propose a new approach for the detection of broken time-reversal symmetry and valley imbalance in monolayer WSe2 based on second-harmonic generation. At room temperature, our method can selectively probe a net valley imbalance generated by ultrafast, coherent and valley-exclusive optical Stark and Bloch–Siegert effects. This work demonstrates the potential and unique capabilities of nonlinear optics as a probe of broken time-reversal symmetry as well as a tool for ultrafast and non-destructive valleytronic operations.