Thickness dependent transition from the 1T$^\prime$ to Weyl semimetal phase in ultrathin MoTe$ _{2} $: Electrical transport, Noise and Raman studies

TL;DR

This study investigates the phase transition from 1T' to Weyl semimetal in ultrathin MoTe2, revealing thickness-dependent electronic and vibrational properties through electrical, noise, and Raman measurements.

Contribution

It provides the first detailed analysis of phase transition and transport properties in ultrathin MoTe2, highlighting thickness-dependent phenomena not observed in bulk materials.

Findings

Thickness-dependent transition temperatures at 208 K and 178 K.

Observation of electron-phonon interaction effects in Raman spectra.

Resistivity behavior indicating electron-electron interactions at low temperatures.

Abstract

Bulk 1T$^\prime$-MoTe$_2$ shows a structural phase transition from 1T$^\prime$ to Weyl semimetallic (WSM) $ T_{d} $ phase at $\sim$ 240 K. This phase transition and transport properties in the two phases have not been investigated on ultra-thin crystals. Here we report electrical transport, $1/f$ noise and Raman studies in ultra-thin 1T$^\prime$-MoTe$_2$ ($\sim$ 5 to 16 nm thick) field-effect transistors (FETs) devices as a function of temperature. The electrical resistivities for thickness 16 nm and 11 nm show maxima at temperatures 208 K and 178 K, respectively, making a transition from semiconducting to semi-metallic phase, hitherto not observed in bulk samples. Raman frequencies and linewidths for 11nm thick crystal show change around 178 K, attributed to additional contribution to the phonon self-energy due to enhanced electron-phonon interaction in the WSM phase. Further, the resistivity at low-temperature shows an upturn below 20 K along with the maximum in the power spectral density of the low frequency $1/f$ noise. The latter rules out the metal-insulator transition (MIT) being responsible for the upturn of resistivity below 20 K. The low temperature resistivity follows $\rho \propto 1/T$, changing to $\rho \propto T$ with increasing temperature supports electron-electron interaction physics at electron-hole symmetric Weyl nodes below 20 K. These observations will pave the way to unravel the properties of WSM state in layered ultra-thin van der Waals materials.