Atomlike interaction and optically tunable giant band-gap renormalization in large-area atomically thin ${\mathrm{MoS}}_2$

Coulomb interactions in atomically thin transition metal dichalcogenides can be dynamically engineered by exploiting the dielectric environment to control the optical and electronic properties. Here we demonstrate an optically tunable giant band-gap renormalization (BGR) $\sim 1200$ and 850 meV from the edge of the conduction band and complete suppression of the exciton absorption in large-area single-layer (1L) and three-layer (3L) ${\mathrm{MoS}}_2$, respectively. The observed giant BGR is two orders of magnitude larger than that in the conventional semiconductors, and it persists for tens of ps. Strikingly, our results demonstrate photoinduced transparency at the electronic band gap using an intense optical field at room temperature. Exciton bleach recovery in 1L and 3L show a contrasting fluence-dependent response, demonstrating the layer-dependent optical tuning of exciton lifetime in a way that would be both reversible and real time. We find that the optical band gap (exciton resonance peak) shows a transient redshift followed by an anomalous blueshift from the lowest energy point as a function of the photo-generated carrier density. The observed exciton energy shift is analogous to atom-atom interactions, and it varies as a Lennard-Jones like potential as a function of the interexciton separation.

Figure 1

Optical microscopic image of CVD grown 1L ${\mathrm{MoS}}_2$ on sapphire crystal shows uniformity in the large scale. (b) Raman spectra and (c) PL spectra of 1L (blue) and 3L (red) ${\mathrm{MoS}}_2$. (d) Ground-state optical absorption of 1L (blue) and 3L (red) ${\mathrm{MoS}}_2$. (e) Electronic band structure calculated using ${\mathrm{G}}_0{\mathrm{W}}_0$ (blue) and DFT (red). (f) Absorption spectrum obtained by solving BSE for 1L (blue) and 3L (red) ${\mathrm{MoS}}_2$.

Figure 2

Color-coded DA spectrum as a function of carrier density showing drastic spectral change above Mott density for (a) 1L and (b) 3L ${\mathrm{MoS}}_2$. The absorbance spectra without (black) and with (red) pump showing the complete suppression of A and B exciton resonance at 440 $\mu \mathrm{J}/{\mathrm{cm}}^2$ for (c) 1L and (d) 3L ${\mathrm{MoS}}_2$. Spectral view of DA for two extreme fluences at pump-probe delay 1 ps for (e) 1L and (f) 3L ${\mathrm{MoS}}_2$. Decay kinetics of A exciton for two extreme fluences (only two extreme fluence data is shown for clarity) of (g) 1L and (h) 3L ${\mathrm{MoS}}_2$.

Figure 3

(a) Calculated optical absorption spectrum for different values of the pump fluence. The black to red line corresponds to the fluence value from 38 to 380 $\mu \mathrm{J}/{\mathrm{cm}}^2$, and the different curves are shifted vertically for clarity. The black arrow highlights the redshift of the A exciton peak with increasing pump fluence. (b) Shift in A exciton resonance calculated from theory (1L) and experiment (1L and 3L) (c) Shift of exciton energy with variation of average exciton distance with the fitting by Lennard-Jones like potential with modified exponent (red solid curve).