Abstract
We study symmetry-broken phases in twisted bilayer graphene at small filling above charge neutrality and at van Hove filling. We argue that the Landau functionals for the particle-hole order parameters at these fillings both have an approximate SU(4) symmetry, but differ in the sign of quartic terms. We determine the order parameter manifold of the ground state and analyze its excitations. For small fillings, we find a strong first-order transition to an SU(3) - U(1) manifold of orders that break spin-valley symmetry and induce a 3-1 splitting of fermionic excitations. For van Hove filling, we find a weak first-order transition to an SU(2) - SU(2) - U(1) manifold of orders that preserves the twofold band degeneracy. We discuss the effect of particle-hole orders on superconductivity and compare with strong-coupling approaches.
| Original language | English (US) |
|---|---|
| Article number | 227601 |
| Journal | Physical review letters |
| Volume | 128 |
| Issue number | 22 |
| DOIs | |
| State | Published - Jun 3 2022 |
Bibliographical note
Funding Information:We thank R. Fernandes, L. Levitov, H. Polshyn, G. Tarnopolsky, O. Vafek, A. Vainshtein, and A. Vishwanath for fruitful discussions. The work by D. V. C. and A. V. C. was supported by U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0014402. L. C. was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, under Contract No. DE-SC0012704. Y. W. was supported by NSF under Award No. DMR-2045871. D. V. C. and A. V. C. also acknowledge the hospitality of KITP at Santa Barbara. The part of research done at KITP was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958. D. V. C. gratefully acknowledges support from Doctoral Dissertation and Larkin Fellowships at the University of Minnesota.
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