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Title: Valley magnetism, nematicity, and density wave orders in twisted bilayer graphene

Journal Article · · Physical Review. B

Herein, we analyze density wave and Pomeranchuk orders in twisted bilayer graphene. This complements our earlier analysis of the pairing instabilities. We assume that near half filling of either conduction or valence band, the Fermi level is close to Van Hove points, where the density of states diverges, and study potential instabilities in the particle-hole channel within a patch model with two valley degrees of freedom. The hexagonal symmetry of twisted bilayer graphene allows for either six or twelve Van Hove points. We consider both cases and find the same two leading candidates for particle-hole order. One is an SU(2)-breaking spin state with ferromagnetism within a valley. A subleading intervalley hopping induces antiferromagnetism between the valleys. The same state has also been obtained in strong-coupling approaches, indicating that this order is robust. The other is a mixed state with 120° complex spin order and orthogonal complex charge order. In addition, we find a weaker but still attractive interaction in nematic channels, and discuss the type of a nematic order.

Research Organization:
Brookhaven National Laboratory (BNL), Upton, NY (United States); Univ. of Minnesota, Minneapolis, MN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); Humboldt Foundation
Grant/Contract Number:
SC0012704; SC0014402
OSTI ID:
1670668
Alternate ID(s):
OSTI ID: 1660737; OSTI ID: 1804111
Report Number(s):
BNL-219920-2020-JAAM; TRN: US2203868
Journal Information:
Physical Review. B, Vol. 102, Issue 12; ISSN 2469-9950
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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Cited By (10)

Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene journal August 2021
Current switching of valley polarization in twisted bilayer graphene journal March 2021
Towards the hidden symmetry in Coulomb interacting twisted bilayer graphene: renormalization group approach text January 2020
Correlated Insulating Phases in the Twisted Bilayer Graphene text January 2020
Optical response and nonlinear Hall response of twisted bilayer graphene in the insulating state preprint January 2020
$SU(4)$ Valley + Spin Fluctuation Interference Mechanism for Nematic Order in Magic Angle Twisted Bilayer Graphene: Impact of Vertex Corrections text January 2020
Symmetry constraints on superconductivity in twisted bilayer graphene: Fractional vortices, $4e$ condensates or non-unitary pairing preprint January 2020
Strain-induced quantum phase transitions in magic angle graphene text January 2020
Charge-$4e$ superconductivity from multi-component nematic pairing: Application to twisted bilayer graphene text January 2021
Spin-triplet superconductivity at the onset of isospin order in biased bilayer graphene text January 2022