Electronic bandstructure renormalization in strained monolayer transitional metal dichalcogenides under optical excitation

Monolayer transition metal dichalcogenides (ML-TMDs), specifically molybdenum disulfide (MoS₂), is subject to nanoscale strain by laying it over a nanoscale-corrugated Au(111) substrate. Scanning tunneling microscopy (STM) reveals that the flexible MoS₂ monolayer conformally adheres to the substrate's nanotopography, resulting in localized regions of high strain at corrugation boundaries. These highly strained regions exhibit significant band structure modifications, characterized by a reduction in the conduction band energy and an elevation of the valence band, creating potential wells that effectively confine photoexcited quasiparticles (QPs), including free charge carriers and excitons. Through systematic STM differential conductance mapping under optical illumination, we observe pronounced renormalization of the local quasiparticle density of states (LDOS) as a function of wavelength and intensity of linearly polarized light within these strain-induced potential wells. [A. Park et al., ACS Nano (2024); DOI: 10.1021/acsnano.4c07448] Additionally, we investigate the response of ML-TMDs to optical vortex beams carrying orbital angular momentum (OAM), and find that illumination with finite photonic OAM leads to the generation of Rydberg excitons and photoexcited QPs with angular momentum. This work provides insights into nanoscale strain engineering of ML-TMDs and their optoelectronic responses, with implications for future quantum photonic and optoelectronic devices.