Symmetry induced phonon renormalization in few layers of 2H-MoTe$_2$ transistors: Raman and first-principles studies

摘要: Understanding of electron-phonon coupling (EPC) in two dimensional (2D) materials manifesting as phonon renormalization is essential to their possible applications nanoelectronics. Here we report in-situ Raman measurements electrochemically top-gated 2, 3 and 7 layered 2H-MoTe$ _{2} $ channel based field-effect transistors (FETs). While the E$ ^{1}_{2g} B$ _{2g} modes exhibit frequency softening linewidth broadening with hole doping concentration (\textit{p}) up $\sim$ 2.3 $\times$10$ ^{13} $/cm$ ^{2} $, A$ _{1g}$ shows relatively small hardening sharpening. The dependence mode on number layers these 2D crystals confirms that occurs primarily top layers, agreement recent predictions. We present first-principles density functional theory (DFT) analysis bilayer MoTe$ qualitatively captures our observations, explain a stronger holes or compared _{1g} originates from in-plane orbital character symmetry states at valence band maximum (VBM). contrast between manifestation EPC monolayer MoS$ those observed here few-layered demonstrates role phonons electronic determining isostructural systems.