In situ nano-optical and tunneling characterization of quantum phases in TMDs

In the monolayer, the transition metal dichalcogenides (TMD) host strongly bound exciton states. The strong light-matter interaction of these excitons, combined with large tunability via interaction with electronic and vibronic degrees of freedom have made this a hot topic in semiconductor research including observations of single-photon emitting quantum dot states and multi-exciton correlations. While these powerful connections between different material properties provide a rich physical landscape, it also poses challenges for study. Nanoscale optical probes have shown large variations in exciton emission energy and intensity that correlates with changes in the lattice and dielectric environment. Further, scanning tunneling microscopy has shown the emergence of deep localized electronic associated with structural deformations. For a full characterization, however, optical signatures must be correlated with the lattice down to the nanometer or even atomic scale. In this presentation we will demonstrate the use of a newly built low-temperature scanning tunneling microscope integrated with a nano-optical probe allowing for co-localized near-field light delivery with high intensity, with scanning tunneling current measurements. We will show the application of this tool to the monolayer TMDs, studying how the STS spectra evolve as a function of optical pump intensity.