High pressure anomalies in exfoliated $MoSe_2$: Resonance Raman and X-ray diffraction studies

TL;DR

This study investigates high pressure effects on exfoliated MoSe2 using resonance Raman and X-ray diffraction, revealing phase transitions, electronic topological transition, and structural changes at specific pressures.

Contribution

It provides detailed insights into pressure-induced phase and electronic transitions in exfoliated MoSe2, highlighting the role of strain in its properties.

Findings

Presence of triclinic phase alongside hexagonal phase at ambient conditions.

Identification of slope changes in Raman modes at 13 GPa and 33 GPa.

Observation of electronic topological transition at 13 GPa.

Abstract

Detailed high pressure Resonance Raman ($RR$) Spectroscopy and X-ray diffraction ($XRD$) studies are carried out on 3-4 layered $MoSe_2$ obtained by liquid exfoliation. Analysis of ambient $XRD$ pattern and $RR$ spectra indicate the presence of a triclinic phase along with its parent hexagonal phase. Pressure evolution of prominent Raman modes and their full width at half maximum ($FWHM$) show slope changes at about 13 GPa and 33 GPa, respectively. Slope change in the linear behavior of reduced pressure ($H$) with respect to Eulerian strain ($f_E$) is observed at about 13 GPa. A minimum in the $FWHM$ values of $E_{2g}^1$ and $A_{2u}^2$ modes at the same pressure indicate to an electronic topological transition ($ETT$). Above 33 GPa the sample completely gets converted to the triclinic structure, which indicates the importance of strain in structural as well as electronic properties of two dimensional materials.