Positive magnetoresistance and chiral anomaly in exfoliated type-II Weyl semimetal $T_\mathrm{d}$-WTe$_{2}$

TL;DR

This study investigates exfoliated $T_ ext{d}$-WTe$_2$, revealing large positive magnetoresistance and chiral anomaly linked to Fermi surface anisotropy, with implications for topological Weyl semimetals.

Contribution

It provides experimental evidence of positive magnetoresistance and chiral anomaly in exfoliated $T_ ext{d}$-WTe$_2$, highlighting the role of Fermi surface anisotropy in these phenomena.

Findings

Transverse magnetoresistance of ~1200% at 5K and 7T.

Confirmation of chiral anomaly via in-plane magnetotransport.

Fermi liquid behavior observed below 50K.

Abstract

Layered van der Waals semimetallic $T_\mathrm{d}$-WTe$_{2}$, exhibiting intriguing properties which include non-saturating extreme positive magnetoresistance (MR) and tunable chiral anomaly, has emerged as model topological type-II Weyl semimetal system. Here, $\sim$45 nm thick mechanically exfoliated flakes of $T_\mathrm{d}$-WTe$_{2}$ are studied $via$ atomic force microscopy, Raman spectroscopy, low-$T$/high-$\mu_{0}H$ magnetotransport measurements and optical reflectivity. The contribution of anisotropy of the Fermi liquid state to the origin of the large positive transverse $\mathrm{MR}_\perp$ and the signature of chiral anomaly of the type-II Weyl fermions are reported. The samples are found to be stable in air and no oxidation or degradation of the electronic properties are observed. A transverse $\mathrm{MR}_\perp$ $\sim$1200\,\% and an average carrier mobility of $5000$\, cm$^{2}$V$^{-1}$s$^{-1}$ at $T=5\,\mathrm{K}$ for an applied perpendicular field $\mu_{0}H_{\perp} = 7\,\mathrm{T}$ are established. The system follows a Fermi liquid model for $T\leq50\,\mathrm{K}$ and the anisotropy of the Fermi surface is concluded to be at the origin of the observed positive MR. The anisotropy of the electronic behaviour is also confirmed by optical reflectivity measurements. The relative orientation of the crystal axes and of the applied electric and magnetic fields is proven to give rise to the observed chiral anomaly in the in-plane magnetotransport.