Substrate-dependent synergistic many-body effects in atomically thin two-dimensional WS2

Mott transition has been realized in atomically thin monolayers (MLs) of two-dimensional (2D) semiconductors ($\mathrm{W}{\mathrm{S}}_{2}$) via optically excited carriers above a critical carrier density through many-body interactions. The above nonlinear optical transition occurs when excited electron hole pairs in the ML $\mathrm{W}{\mathrm{S}}_{2}$ continuum heavily interact with each other followed by transformation into a collective electron-hole-plasma phase, by losing their identity as individual quasiparticles. This is manifested by the alluring redshift-blueshift crossover phenomena of the excitonic peaks in the emission spectra, resulting from the synergistic attraction-repulsion processes at the Mott transition point. A systematic investigation of many-body effects is reported on ML $\mathrm{W}{\mathrm{S}}_{2}$, while considering the modulated dielectric screening of three different substrates, viz., silicon dioxide, sapphire, and gold. Substrate doping effects on ML $\mathrm{W}{\mathrm{S}}_{2}$ are discussed using the Raman fingerprints and photoluminescence spectral weight, which are further corroborated using theoretical density functional theory calculations. Further, the substrate-dependent excitonic Bohr radius of ML $\mathrm{W}{\mathrm{S}}_{2}$ is extracted via modeling the emission energy shift with Lennard-Jones potential. The variation of the Mott point, as well as the excitonic Bohr radius, is explained via the substrate-induced dielectric screening effect for both dielectric substrates, which is, however, absent in ML $\mathrm{W}{\mathrm{S}}_{2}$ on Au. In this paper, we therefore reveal diverse many-body ramifications in 2D semiconductors and offer decisive outlooks on selecting impeccable substrate materials for innovative device engineering.