Symmetry-dependent phonon renormalization in monolayer MoS 2 transistor

A strong electron-phonon interaction which limits the electronic mobility of semiconductors can also have significant effects on phonon frequencies. The latter is the key to the use of Raman spectroscopy for nondestructive characterization of doping in graphene-based devices. Using in situ Raman scattering from a single-layer MoS${}_{2}$ electrochemically top-gated field-effect transistor (FET), we show softening and broadening of the ${A}_{1g}$ phonon with electron doping, whereas the other Raman-active ${E}_{2g}^{1}$ mode remains essentially inert. Confirming these results with first-principles density functional theory based calculations, we use group theoretical arguments to explain why the ${A}_{1g}$ mode…