Observation of Ferromagnetic Phase in the Second Moir\'e Band of Twisted MoTe2

TL;DR

This paper reports the discovery of a ferromagnetic phase in the second moiré band of twisted bilayer MoTe2, tunable by doping and displacement field, indicating time-reversal symmetry-breaking in higher moiré bands.

Contribution

It provides the first experimental observation of ferromagnetism in the second moiré band of twisted MoTe2, expanding understanding of magnetic states in moiré materials.

Findings

Ferromagnetic phase observed at 2.58 holes per moiré unit cell.

Curie temperature of the ferromagnetic phase is 3.5 K.

Displacement field can suppress the ferromagnetic phase.

Abstract

Flat bands and electron correlation in moir\'e lattices give rise to many exotic phases, including Mott insulators, superconductivity, and topological states. Within the first moir\'e band, integer and fractional quantum anomalous Hall effects have been observed in twisted bilayer MoTe2 (tMoTe2) at one hole doping and fractional doping per moir\'e unit cell, respectively. When the second moir\'e band is fully hole doped, quantum spin Hall insulator has also been reported in tMoTe2 at a certain twist angle. Exotic topological states together with ferromagnetic (FM) states in the high moir\'e band can potentially exist as well. In this study, we report the observation of a FM phase in the second moir\'e band in tMoTe2. The FM phase can be tuned by both the doping level and displacement field. At filling around 2.58 holes per moir\'e unit cell, the FM phase reaches a Curie temperature of 3.5 K. A large displacement field can suppress the FM phase, like the FM phase at the filling of -1. Our results demonstrate the realization of time-reversal symmetry-breaking states in the higher moir\'e bands in tMoTe2.