Nonlinear valley selection rules and all-optical probe of broken time-reversal symmetry in monolayer WSe2
Paul Herrmann, Sebastian Klimmer, Thomas Lettau, Till Weickhardt, Anastasios V. Papavasileiou, Kseniia Mosina, Zdeněk Sofer, Ioannis Paradisanos, Daniil Kartashov, Jan Wilhelm, Giancarlo Soavi
Abstract
Abstract 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 2 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.