Homogeneous linewidth broadening and exciton dephasing mechanism in $\mathrm{MoT}{\mathrm{e}}_2$

Spectroscopic studies of mechanically exfoliated monolayer $\mathrm{MoT}{\mathrm{e}}_2$ were performed over a wide temperature range from 4.2 to 300 K. At a low temperature, the photoluminescence spectra for monolayer $\mathrm{MoT}{\mathrm{e}}_2$ showed two sharp peaks for excitons and charged excitons (trions). The homogeneous linewidth of the exciton peak broadened linearly as the temperature increased. This linear linewidth broadening was caused by acoustic-phonon scattering of the exciton, i.e., shortening of exciton dephasing. The broadening factor due to exciton–acoustic–phonon interactions was found to be $0.11\mathrm{meV}{\mathrm{K}}^{-1}$. This small value for the exciton–phonon coupling coefficient and the lack of a Stokes shift suggest that exciton–phonon interactions in monolayer $\mathrm{MoT}{\mathrm{e}}_2$ are in the weak coupling regime.

Figure 1

Raman scattering spectra for mechanically exfoliated monolayer, bilayer, trilayer, and bulk $\mathrm{MoT}{\mathrm{e}}_2$ flakes on $\mathrm{Si}{\mathrm{O}}_2\text{/}\mathrm{Si}$ substrates obtained at an excitation wavelength of 532 nm. Left inset: optical microscope image of monolayer and bilayer $\mathrm{MoT}{\mathrm{e}}_2$ on $\mathrm{Si}{\mathrm{O}}_2\text{/}\mathrm{Si}$ substrates. Right inset: frequency shift of the $E_{2\mathrm{g}}^1$ mode as a function of layer thickness.

Figure 2

Temperature dependence of the PL spectra for monolayer $\mathrm{MoT}{\mathrm{e}}_2$ and fitted results obtained using Voigt functions. The PL spectra are normalized by the intensity of the exciton peak. Each spectrum is vertically shifted for clarity.

Figure 3

PL spectra and fitted results for monolayer $\mathrm{MoT}{\mathrm{e}}_2$. (a) Upper panel: PL spectrum (blue line) and spectral fitted result obtained using the sum of Voigt functions (red line) at 4.2 K. Lower panel: each component of the spectral peak. (b) Upper panel: PL spectrum (blue line) and spectral fitted result using the sum of Voigt functions (red line) at room temperature. Lower panel: each component of the spectral peak.

Figure 4

Temperature dependence of the exciton (red solid squares) and trion (blue solid circles) peak positions in PL spectra for monolayer $\mathrm{MoT}{\mathrm{e}}_2$ and fitted lines obtained using the Varshni equation [Eq. (1)].

Figure 5

The FWHM of the exciton peak linewidth in PL spectra for monolayer $\mathrm{MoT}{\mathrm{e}}_2$ plotted as a function of temperature. The solid line represent the fitted results obtained using Eq. (2). The experimental results for three different monolayer $\mathrm{MoT}{\mathrm{e}}_2$ flakes on $\mathrm{Si}{\mathrm{O}}_2\text{/}\mathrm{Si}$ and $\mathrm{Si}{\mathrm{O}}_2$ are shown in the figure.