Atomically thin van der Waals materials provide a versatile and unique platform for exploring novel physical interactions at low dimensionality and enabling new device geometries with tunable functionalities. In this talk, I will present our recent progress in three aspects: understanding many-body screening effects in 2D excitons, developing mechanical detection of magnetic domains, and identifying new types of 2D molecular materials. In the first part, I will discuss how exciton-polaron interactions and Fermi sea screening in the 2D semiconductor evolve while taking into account polaron-polaron interactions. Our result revealed the presence of a critical carrier density for the onset of strongly modified screening, which is beyond the conventional exciton-polaron theory. The second part of the talk will include our most recent results on 2D AFM transition-metal phosphorous trichalcogenides, where we couple the magnetic transitions into the mechanical degree of freedom. We observed the expected steady-state spin transitions based on magnetostriction effects and saw signatures of additional transitions arising from magnetic domain dynamics. In the last part, I will present the optical characterization of spin states in 2D spin-crossover molecular crystals, including the fabrication and the identification of layer-dependent spin-crossover transitions with optical spectroscopies.
