Odd- and even-denominator fractional quantum Hall states in monolayer WSe$_2$

TL;DR

This study reveals fractional quantum Hall states, including odd- and even-denominator types, in monolayer WSe$_2$, demonstrating its potential as a platform for exploring exotic quantum phenomena in 2D materials.

Contribution

First observation of fractional quantum Hall states in monolayer WSe$_2$, including an even-denominator state, with systematic evolution across Landau levels.

Findings

Observation of fractional quantum Hall states in the lowest three Landau levels.

Detection of an even-denominator state potentially hosting non-Abelian anyons.

Systematic evolution of odd-denominator FQH sequences with Landau level index.

Abstract

Monolayer (ML) semiconducting transition-metal dichalcogenides (TMDs) represent a unique class of two-dimensional (2D) electron systems. Their atomically thin structure -- just like graphene -- facilitates gate-tunability, while the sizable band gap and strong spin-orbit coupling hold promise for properties beyond graphene. Measurements under large magnetic fields have revealed an unusual LL structure, distinct from other 2D electron systems. However, owing to limited sample quality and poor electrical contact, probing the lowest Landau levels (LLs) has been challenging, and observation of electron correlations within the fractionally filled LLs regime has not been possible. Here, through bulk electronic compressibility measurements, we investigate the LL structure of ML WSe$_2$ in the extreme quantum limit, and observe fractional quantum Hall (FQH) states in the lowest three LLs. The odd-denominator FQH sequences demonstrate a systematic evolution with the LL orbital index, which has not been observed in any other system but is consistent with generic theoretical expectations. In addition, we observe an even-denominator state in the second LL that is expected to host non-Abelian statistics. Our results suggest that the 2D semiconductors can provide an experimental platform that closely resembles idealized theoretical models in the quantum Hall regime.