Spin and Orbital Metallic Magnetism in Rhombohedral Trilayer Graphene

Abstract

We provide a complete theoretical interpretation of the metallic broken spin/valley symmetry states recently discovered in ABC trilayer graphene (ABC) perturbed by a large transverse displacement field. Our conclusions combine insights from ABC trilayer graphene electronic structure models and mean field theory, and are guided by precise magneto-oscillation Fermi-surface-area measurements. We conclude that the physics of ABC trilayer graphene is shaped by the principle of momentum-space condensation, which favors Fermi surface reconstructions enabled by broken spin/valley flavor symmetries when the single-particle bands imply thin annular Fermi seas. We find one large outer Fermi surface enclosed majority-flavor states and one or more small inner hole-like Fermi surfaces enclosed minority-flavor states that are primarily responsible for nematic order. The smaller surfaces can rotate along a ring of van-Hove singularities or reconstruct into multiple Fermi surfaces with little cost in energy. We propose that the latter property is responsible for the quantum oscillation frequency fractionalization seen experimentally in some regions of the carrier-density/displacement-field phase diagram.

Strong correlations in ABC-stacked trilayer graphene: Moiré is important

“…We note that upon increasing the density into the hole-doped regime a variety of possible broken-symmetry phases may be realized (depending on the displacement field, strength of interactions etc.) [46,47]. In the non-interacting model, for u d > 0, there is a well isolated band which allows a well-defined Chern number to be defined for the valence band, C = ±3, where the sign depends on which valley is being occupied [19,20].…”

“…In this work, we target this specific line of inquiry by quantitatively analyzing the effects of the moiré potential on ABC-stacked trilayer graphene systems. Though recent theoretical works have focused on the various broken symmetry phases and its relation to the observed superconductivity [45][46][47][48][49][50][51][52], a deeper analysis with regard to the influence of the moiré potential has yet to be performed. Motivated by Ref.…”

Spontaneous momentum polarization and diodicity in Bernal bilayer graphene

“…Recently, theoretical works shed light on a new type of Coulomb-driven instability in the quarter and half-metal states of moiréless bilayer and trilayer graphene. Based on a three-pocket model, it is argued that the exchange interaction could induce a spontaneous condensation of charge carriers in the momentum space [21][22][23]. This phenomenon results from the process where carriers flock to occupy one of the trigonal-warping-induced pockets (Fig.…”

Electrical control of magnetism in spin-orbit coupled graphene multilayers

“…Further, the nature of ordering of spin-degrees of freedom in moiré materials has proven difficult to detect and manipulate. Very recently, both orbital and spin ferromagnetism has been observed in few-layered graphene in absence of any moiré pattern [23][24][25][26][27][28][29][30][31]. These remarkable experiments naturally motivate the following questions.…”