01949nas a2200229   4500000000100000000000100001008004100002260002800043100001700071700002300088700002600111700001700137700001900154700001400173700001600187700001200203245011800215856004500333300001100378490000700389520132300396       2020                            d  c10/2020bIOP Publishing1 aSubhadip Das1 aKoyendrila Debnath1 aBiswanath Chakraborty1 aAnjali Singh1 aShivani Grover1 aDVS Muthu1 aUV Waghmare1 aAK Sood00aSymmetry induced phonon renormalization in few layers of 2H-MoTe2 transistors: Raman and first-principles studies  uhttps://doi.org/10.1088/1361-6528/abbfd6  a0452020 v323 aUnderstanding of electron–phonon coupling (EPC) in two-dimensional (2D) materials manifesting as phonon renormalization is essential to their possible applications in nanoelectronics. Here we report in situ Raman measurements of electrochemically top-gated 2, 3 and 7 layered 2H-MoTe2 channel based field-effect transistors. While the and B2g phonon modes exhibit frequency softening and linewidth broadening with hole doping concentration (p) up to ∼2.3 × 1013/cm2, A1g shows relatively small frequency hardening and linewidth sharpening. The dependence of frequency renormalization of the mode on the number of layers in these 2D crystals confirms that hole doping occurs primarily in the top two layers, in agreement with recent predictions. We present first-principles density functional theory analysis of bilayer MoTe2 that qualitatively captures our observations, and explain that a relatively stronger coupling of holes with or B2g modes as compared with the A1g mode originates from the in-plane orbital character and symmetry of the states at valence band maximum. The contrast between the manifestation of EPC in monolayer MoS2 and those observed here in a few-layered MoTe2 demonstrates the role of the symmetry of phonons and electronic states in determining the EPC in these isostructural systems.