Doping controlled Fano resonance in bilayer 1T$ ^{\prime} $-ReS$ _{2} $: Raman experiments and first-principles theoretical analysis

TL;DR

This study combines Raman spectroscopy and first-principles calculations to investigate how electron doping induces Fano resonance and affects vibrational modes in bilayer ReS2, revealing strong electron-phonon coupling linked to structural phase transition.

Contribution

It provides the first detailed analysis of doping-induced Fano resonance in bilayer ReS2 using combined experimental and theoretical approaches.

Findings

Electron doping causes softening and broadening of in-plane vibrational modes.

Fano resonance appears at a doping level of ~3.7×10^{13} cm^{-2}.

Strong electron-phonon coupling is linked to a structural phase transition.

Abstract

In the bilayer ReS$ _{2} $ channel of a field-effect transistor (FET), we demonstrate using Raman spectroscopy that electron doping (n) results in softening of frequency and broadening of linewidth of the in-plane vibrational modes, leaving out-of-plane vibrational modes unaffected. Largest change is observed for the in-plane Raman mode at $\sim$ 151 cm$^{-1} $, which also shows doping induced Fano resonance with the Fano parameter 1/q = -0.17 at doping concentration of $\sim 3.7\times10^{13}$ cm$^{-2} $. A quantitative understanding of our results is provided by first-principles density functional theory (DFT), showing that the electron-phonon coupling (EPC) of in-plane modes is stronger than that of out-of-plane modes, and its variation with doping is independent of the layer stacking. The origin of large EPC is traced to 1T to 1T$ ^{\prime} $ structural phase transition of ReS$ _{2} $ involving in-plane displacement of atoms whose instability is driven by the nested Fermi surface of the 1T structure. Results are also compared with the isostructural trilayer ReSe$ _{2} $.