Interplay between topology and correlations in the second moiré band of twisted bilayer MoTe2

Abstract

Topological flat bands formed in two-dimensional lattice systems offer an opportunity to study fractional phases of matter in the absence of an external magnetic field. Examples include fractional quantum anomalous Hall effects and fractional topological insulators. Recently, fractional quantum anomalous Hall effects have been experimentally realized in both twisted bilayer MoTe2 and rhombohedral-stacked multilayer graphene on hexagonal boron nitride. These studies focus mainly on the first moiré flat band, but there is a possibility that non-Abelian states could occur in the second moiré band. Here we present a systematic transport study of twisted bilayer MoTe2 devices, focusing on the second moiré band. We observe ferromagnetism in the second moiré band, and a Chern insulator state driven by out-of-plane magnetic fields at a filling factor of three holes per moiré unit cell. Between fillings of 2.2 and 2.7 holes per moiré unit cell, we observe a finite temperature resistivity minimum with a 1/T scaling law at low temperatures and a large out-of-plane negative magnetoresistance. Applying an out-of-plane electric field can induce quantum phase transitions at both integer and fractional filling factors. Our studies lay the groundwork for realizing tunable topological states and other unexpected magnetic phases beyond the first moiré flat band based in twisted MoTe2. It may be possible to find non-Abelian electronic states in the higher bands of flat-band materials. Now a detailed transport study of the second moiré band of twisted bilayer MoTe2 maps out several topological and magnetic states.