Tailoring the Phase Transition and Electron-Phonon Coupling in 1T'-MoTe2 by Charge Doping: A Raman Study

TL;DR

This study investigates how charge doping influences phase transitions and electron-phonon interactions in 1T'-MoTe2 flakes, revealing the stabilization of specific phases at room temperature and the evolution of electron-phonon coupling with thickness and doping.

Contribution

It demonstrates experimentally that charge doping can stabilize desired phases of 1T'-MoTe2 at room temperature and explores how electron-phonon coupling varies with flake thickness and doping levels.

Findings

Charge doping stabilizes specific phases at room temperature.

Phase transition suppression in flakes thinner than 10 nm.

Electron-phonon coupling signatures vary with thickness and doping.

Abstract

Transition metal dichalcogenides (TMDs) are a class of widely studied 2D layered materials which exist in various polymorphs. The 1T' phase of MoTe2 is of prime importance as it has been reported to show quantum spin hall (QSH) behavior with a fairly large band-gap of ~ 60 meV, in contrast to most QSH materials known. It is noteworthy that though the monolayer 1T'-MoTe2 was initially predicted to show the QSH behavior, recent theoretical studies claim that the few-layered counterparts also exhibit higher order topological behavior. Besides, 1T'-MoTe2 also undergoes a hysteretic phase transition to the Td phase (which is a type-II Weyl semimetal) by breaking the inversion symmetry of the crystal. While the phase transition between these two topological phases is of utmost importance, its study has been mostly restricted to bulk single crystal flakes, thereby not sufficiently exploring the effect of dimensionality. We have studied the phase transition in 1T'-MoTe2 as a function of flake-thickness. Though our Raman studies show a suppression of the phase transition in the thin (thickness <10 nm) flakes [similar to the report Phys. Rev. B 97, 041410 (2018)], we have experimentally demonstrated the possibility of stabilizing the desired phase (1T' or Td) at room temperature by charge doping. Further, we have observed clear signatures of electron-phonon coupling in MoTe2, which evolves as a function of flake-thickness and charge doping.