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.