Special Seminar: Owen Sheekey – UCSB: Inter-valley coherence, intrinsic and extrinsic spin-orbit coupling in rhombohedral graphene

Abstract: Rhombohedral graphene multilayers provide a clean and highly reproducible platform to explore the emergence of superconductivity and magnetism in a strongly interacting electron system. The high density of states near the van Hove singularities lead to a variety of broken symmetry phases – including exotic forms of spin and valley ferromagnetism [2, 3]. Because of their combined spin and valley ‘isospin’ degrees of freedom, these Stoner magnets exhibit an approximate SU(4) symmetry with a near degeneracy in the many body phase diagram. In reality, this SU(4) symmetry is only approximate, weak symmetry breaking arises even at the single particle level – in the form of intrinsic spin-orbit coupling. Here, we use high resolution thermodynamic compressibility measurements and nanoSQUID on tip (nSOT) magnetometry to study the effects that intrinsic spin-orbit coupling has on the magnetic phase diagram in rhombohedral graphene. By supporting rhombohedral graphene on a WSe2 substrate, ‘extrinsic’ strong spin-orbit coupling can be proximitized, significantly altering the magnetic phase diagram. We demonstrate the presence of an inter-valley coherent quarter metal which becomes strongly spin-valley locked when supported by WSe2. Our results shed light on the role proximity induced Ising spin-orbit coupling and intrinsic spin-orbit coupling plays in selecting the ground state in correlated graphene systems.

References:

[1] Zhou, H., Xie, T., Taniguchi, T. et al. Nature 598, 434–438 (2021).

[2] Zhou, H., Xie, T., Ghazaryan, A., et al. Nature 598, 429–433 (2021).

[3] Arp, T., et. al. arXiv:2310.03781 (2023).