Universal Magnetic Phases in Twisted Bilayer MoTe$_2$

TL;DR

This study maps the magnetic phases of twisted bilayer MoTe$_2$, revealing a universal ferromagnetic phase across various twist angles and uncovering the complex interplay between magnetism, topology, and electronic band structure.

Contribution

It provides the first systematic mapping of magnetic phases in tMoTe$_2$ across twist angles using local optical and magnetometry techniques, highlighting a universal ferromagnetic phase.

Findings

Spontaneous ferromagnetism at specific filling factors across a wide twist angle range

Observation of twist-angle-dependent Curie temperatures indicating different magnetic interactions

No clear topological gap at certain fillings despite broken time-reversal symmetry

Abstract

Twisted bilayer MoTe$_2$ (tMoTe$_2$) has emerged as a robust platform for exploring correlated topological phases, notably supporting fractional Chern insulator (FCI) states at zero magnetic field across a wide range of twist angles. The evolution of magnetism and topology with twist angle remains an open question. Here, we systematically map the magnetic phase diagram of tMoTe$_2$ using local optical spectroscopy and scanning nanoSQUID-on-tip (nSOT) magnetometry. We identify spontaneous ferromagnetism at moir\'e filling factors $\nu = -1$ and $-3$ over a twist angle range from 2.1$^\circ$ to 3.7$^\circ$, revealing a universal, twist-angle-insensitive ferromagnetic phase. At 2.1$^\circ$, we further observe robust ferromagnetism at $\nu = -5$, absent in the devices with larger twist angle -- a signature of the flattening of higher bands in this twist angle range. Temperature-dependent measurements reveal a contrasting twist-angle dependence of the Curie temperatures between $\nu = -1$ and $\nu = -3$, indicating distinct interplay between exchange interaction and bandwidth for the two Chern bands. Despite spontaneous time-reversal symmetry breaking, we find no evidence of a topological gap at $\nu = -3$; however, fragile correlated topological phases could be obscured by the device disorder evident in our spatially resolved measurements. Our results establish a global framework for understanding and controlling magnetic order in tMoTe$_2$ and highlight its potential for accessing correlated topological phases in higher energy Chern band.