Probing valley population imbalance in TMDs with T-dependent SHG*

Valleys in transition metal dichalcogenides (TMDs) provide an additional degree of freedom that can be used for information transport and storage. When TMDs interact with intense laser light, the SHG-field inherits characteristics that reflect not only the broken inversion symmetry in real space, but also the valley anisotropy in reciprocal space. The latter is present whenever there exists a valley population imbalance (VPI) between the two valleys and affects the polarization state of the detected SHG. In this work, it is shown that the temperature-induced change of the SHG intensity dependence on the excitation field polarization, is a unique fingerprint of VPI. In particular, VPI mapping based on polarization-resolved raster-scanning imaging microscopy was performed inside a cryostat to generate the SHG contrast in the presence of VPI, from every point of a TMD flake. The generated contrast is marked by rotation of the SHG intensity polar diagrams at low temperatures and is attributed to the VPI-induced SHG.