Breakdown of compensation and persistence of non-saturating magnetoresistance in WTe2 thin flakes

TL;DR

This study investigates the magnetoresistance behavior in thin WTe2 flakes, revealing that electron-hole compensation is not the primary cause of their extremely large, non-saturating magnetoresistance, challenging previous assumptions.

Contribution

It provides a detailed analysis of magnetoresistance and Hall effects in thin WTe2, showing compensation breakdown and persistence of large MR under doping, which is a novel insight.

Findings

Quantum oscillations observed in thin WTe2

Magnetoresistance exceeds 2 x 10^4% at 14 T

Electron-hole compensation not essential for large MR

Abstract

We present a detailed study of magnetoresistance \r{ho}xx(H), Hall effect \r{ho}xy(H), and electrolyte gating effect in thin (<100 nm) exfoliated crystals of WTe2. We observe quantum oscillations in H of both \r{ho}xx(H) and \r{ho}xy(H), and identify four oscillation frequencies consistent with previous reports in thick crystals. \r{ho}xy(H) is linear in H at low H consistent with near-perfect electron-hole compensation, however becomes nonlinear and changes sign with increasing H, implying a breakdown of compensation. A field-dependent ratio of carrier concentrations p/n can consistently explain \r{ho}xx(H) and \r{ho}xy(H) within a two-fluid model. We also employ an electrolytic gate to highly electron-dope WTe2 with Li. The non-saturating \r{ho}xx(H) persists to H = 14 T with magnetoresistance ratio exceeding 2 x 104 %, even with significant deviation from perfect electron-hole compensation (p/n = 0.84), where the two-fluid model predicts a saturating \r{ho}xx(H). Our results suggest electron-hole compensation is not the mechanism for extremely large magnetoresistance in WTe2, other alternative explanations need to be considered.