Measurement of the complex valley polarization second order nonlinear susceptibility

The spread of valleytronic devices based on 2d materials is limited mostly by the absence of suitable methods to detect the valley degree of freedom. Current detection of the valley polarization (VP) is based on polarized photoluminescence, a slow and destructive method, only recently second harmonic generation (SHG) has been proposed as an alternative, with benefits thanks to its ultrafast and non-destructive nature [1]. However, current detection schemes for valley SHG measure a small rotation angle in the SHG polarization and are limited in detection efficiency as well as valley addressability.

We propose a new approach to detect the VP, based on measuring the total SHG intensity while tuning the excitation from linear to circular polarized. This method not only probes the disperion of the valley-induced susceptibility across the excitonic A1s resonance, but we also demonstrate the significance of interference between the electric-dipole (ED) and the valley-induced susceptibilities, in analogy with the magnetic-ED interference in bulk magnets [2].

[1] Herrmann, P. et al.: small 2023

[2] Fiebig, M. et al.: PRL 1994 73(2127)