  Mott transition has been realized in atomically thin monolayer (ML) of two
dimensional semiconductors (WS$_2$) 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 ML WS2 continuum
heavily interact with each other followed by transformation into a collective
electron hole plasma phase (EHP), by losing their identity as individual
quasiparticles. This is manifested by the alluring red-shift-blue-shift
crossover (RBC) 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 WS$_2$, while considering the modulated dielectric screening of
three different substrates, viz., silicon dioxide, sapphire, and gold.
Substrate doping effects on ML WS$_2$ are discussed using the Raman
fingerprints and PL spectral weight, which are further corroborated using
theoretical DFT calculations. Further the substrate dependent excitonic Bohr
radius of ML WS$_2$ is extracted via modelling the emission energy shift with
Lennard-Jones potential. The variation of Mott point as well as excitonic Bohr
radius is explained via substrate induced dielectric screening effect for both
the dielectric substrates, which is however absent in ML WS$_2$ on Au. Our
study therefore reveals diverse many-body ramifications in 2D semiconductors
and offers decisive outlooks on selecting the impeccable substrate materials
for innovative device engineering.

Materials Science;Mesoscale and Nanoscale Physics