Using first-principles calculations we show that the band gap of bilayer
sheets of semiconducting transition metal dichalcogenides (TMDs) can be reduced
smoothly by applying vertical compressive pressure. These materials undergo a
universal reversible semiconductor to metal (S-M) transition at a critical
pressure. S-M transition is attributed to lifting the degeneracy of the bands
at fermi level caused by inter-layer interactions via charge transfer from
metal to chalcogens. The S-M transition can be reproduced even after
incorporating the band gap corrections using hybrid functionals and GW method.
The ability to tune the band gap of TMDs in a controlled fashion over a wide
range of energy, opens-up possibility for its usage in a range of applications.