Spin-orbit driven ferromagnetism at half moir\'e filling in magic-angle twisted bilayer graphene

TL;DR

This study demonstrates how spin-orbit coupling induces ferromagnetism in magic-angle twisted bilayer graphene at half filling, revealing tunable topological and magnetic properties driven by electron correlation and SOC.

Contribution

It provides experimental evidence that SOC transforms correlated insulating states into ferromagnets in twisted bilayer graphene, enabling control over topological properties.

Findings

SOC induces ferromagnetism at half moiré filling.

Magnetic order is tunable with magnetic and electric fields.

SOC influences isospin order and superconductivity stability.

Abstract

Strong electron correlation and spin-orbit coupling (SOC) provide two non-trivial threads to condensed matter physics. When these two strands of physics come together, a plethora of quantum phenomena with novel topological order have been predicted to emerge in the correlated SOC regime. In this work, we examine the combined influence of electron correlation and SOC on a 2-dimensional (2D) electronic system at the atomic interface between magic-angle twisted bilayer graphene (tBLG) and a tungsten diselenide (\WSe) crystal. In such a structure, strong electron correlation within the moir\'e flatband stabilizes correlated insulating states at both quarter and half-filling, whereas SOC transforms these Mott-like insulators into ferromagnets, evidenced by robust anomalous Hall effect with hysteretic switching behavior. The coupling between spin and valley degrees of freedom is unambiguously demonstrated as the magnetic order is shown to be tunable with an in-plane magnetic field, or a perpendicular electric field. In addition, we examine the influence of SOC on the isospin order and stability of superconductivity. Our findings establish an efficient experimental knob to engineer topological properties of moir\'e bands in twisted bilayer graphene and related systems.