Isospin- and momentum-polarized orders in bilayer graphene

Abstract

Electron bands in the untwisted bilayer graphene flatten out in a transverse electric field, offering a promising platform for correlated electron physics. We predict that the spin/valley isospin magnetism, resembling that seen in moire bands, coexists with momentum-polarized phases occurring via a "flocking transition" in momentum space in which the electron distribution is spontaneously displaced in momentum space relative to the K or K valley centers. These phases feature unusual observables such as persistent currents in the ground state. Momentum-polarized carriers "sample" the Berry curvature of the conduction band, resulting in a unique behavior of the anomalous Hall conductivity and other effects that do not occur in previously studied systems.

Non-Abelian topological superconductivity in maximally twisted double-layer spin-triplet valley-singlet superconductors

“…While our assumption of a dominant pairing interaction in the f-wave channel for spin-triplet SC2 phase of RTG/BBG is supported by proposals based on acoustic phonons 36,37 and renormalization group analysis 66 , some recent works suggest an alternative possibility of chiral p ± ip 0 pairing symmetry [67][68][69] , which is also compatible with the phenomenology of the SC2 phase. In Supplementary Note 8 we present a detailed analysis of pairing instabilities in all possible pairing channels in maximally twisted double-layer RTG/BBG.…”

Spontaneous momentum polarization and diodicity in Bernal bilayer graphene

“…According to the n − D map, the high-density boundary of the fully momentum-polarized state, M P , occurs around n = −0.06 × 10 12 cm −2 at D = 300 mV/nm. This is the same order of magnitude compared to the estimated density range where the three-pocket model is applicable [21]. In the following, we show that the momentum space instability persists outside of this density regime in the presence of a large Fermi surface (Fig.…”

“…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.…”

“…According to the theoretical model, spontaneous momentum polarization in BLG is described by a characteristic phase diagram, as shown in Fig. 1d [21]. Different colors in the schematic diagram mark regimes where 1, 2, 3, and 4 Fermi pockets are sequentially occupied as charge carriers are added to the system.…”

“…2b-c, the maximum positive (or negative) nonlinear response always occurs near the black dashed lines in the polar-coordinate plots, which is in excellent agreement with the expected behavior of momentum po-larization. Based on the value of β 1 , the n − D map divides into distinct regimes marked by A, B, A , B and C. The transition boundary between A and B (A and B ) shifts to higher carrier density with increasing D. This gives rise to a fan-like diagram that is characteristic of momentum polarization [21].…”