Lattice collective modes from a continuum model of magic-angle twisted bilayer graphene
Abstract
Here, we show that the insulating states of magic-angle twisted bilayer graphene support a series of collective modes corresponding to local particle-hole excitations on triangular lattice sites. Our theory is based on a continuum model of the magic angle flat bands. When the system is insulating at moiré band filling ν = -3, our calculations show that the ground state supports seven low-energy modes that lie well below the charge gap throughout the moiré Brillouin zone, one of which couples strongly to THz photons. The low-energy collective modes are faithfully described by a model with a local SU(8) degree of freedom in each moiré unit cell that we identify as the direct product of spin, valley, and an orbital pseudospin. Apart from spin and valley-wave modes, the collective mode spectrum includes a low-energy intraflavor exciton mode associated with transitions between flat valence and conduction band orbitals.
- Publication Date:
- Research Org.:
- Univ. of Texas, Austin, TX (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC); National Science Foundation (NSF)
- OSTI Identifier:
- 1849402
- Grant/Contract Number:
- FG02-02ER45958; DMR-1720595
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Physical Review. B
- Additional Journal Information:
- Journal Volume: 104; Journal Issue: 3; Journal ID: ISSN 2469-9950
- Publisher:
- American Physical Society (APS)
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; materials science; physics; quasiparticles & collective excitations; graphene; Mott insulators; Hartree-Fock methods; random phase approximation
Citation Formats
Kumar, Ajesh, Xie, Ming, and MacDonald, A. H. Lattice collective modes from a continuum model of magic-angle twisted bilayer graphene. United States: N. p., 2021.
Web. doi:10.1103/physrevb.104.035119.
Kumar, Ajesh, Xie, Ming, & MacDonald, A. H. Lattice collective modes from a continuum model of magic-angle twisted bilayer graphene. United States. https://doi.org/10.1103/physrevb.104.035119
Kumar, Ajesh, Xie, Ming, and MacDonald, A. H. Thu .
"Lattice collective modes from a continuum model of magic-angle twisted bilayer graphene". United States. https://doi.org/10.1103/physrevb.104.035119. https://www.osti.gov/servlets/purl/1849402.
@article{osti_1849402,
title = {Lattice collective modes from a continuum model of magic-angle twisted bilayer graphene},
author = {Kumar, Ajesh and Xie, Ming and MacDonald, A. H.},
abstractNote = {Here, we show that the insulating states of magic-angle twisted bilayer graphene support a series of collective modes corresponding to local particle-hole excitations on triangular lattice sites. Our theory is based on a continuum model of the magic angle flat bands. When the system is insulating at moiré band filling ν = -3, our calculations show that the ground state supports seven low-energy modes that lie well below the charge gap throughout the moiré Brillouin zone, one of which couples strongly to THz photons. The low-energy collective modes are faithfully described by a model with a local SU(8) degree of freedom in each moiré unit cell that we identify as the direct product of spin, valley, and an orbital pseudospin. Apart from spin and valley-wave modes, the collective mode spectrum includes a low-energy intraflavor exciton mode associated with transitions between flat valence and conduction band orbitals.},
doi = {10.1103/physrevb.104.035119},
journal = {Physical Review. B},
number = 3,
volume = 104,
place = {United States},
year = {Thu Jul 08 00:00:00 EDT 2021},
month = {Thu Jul 08 00:00:00 EDT 2021}
}
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