Collective Modes in Magic-Angle Twisted Bilayer Graphene
ORAL
Abstract
We study the collective modes of the correlated insulating states in magic-angle twisted bilayer graphene (MATBG) within the framework of the generalized random phase approximation (GRPA), also known as the time-dependent Hartree-Fock approximation (TDHFA), using a continuum model and assuming insulating states that break spin/valley flavor but not translational symmetries. The calculations confirm the stability of the translationally invariant states and provide values for key energy scales associated with low-energy collective fluctuations, including spin-stiffnesses and gaps for valley-wave modes. We find that zone-boundary collective mode energies are an order of magnitude smaller than the charge gaps. By fitting to the calculated collective excitation spectra, we derive generalized spin models that fully capture the low-energy physics. Finally, we discuss how these collective mode energies vary with moiré band filling factor and the possible role of their coupling to Fermi surface quasiparticles in superconductivity and non-Fermi liquid behavior.
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Presenters
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Ajesh Kumar
University of Texas at Austin, Department of Physics, University of Texas at Austin
Authors
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Ajesh Kumar
University of Texas at Austin, Department of Physics, University of Texas at Austin
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Ming Xie
University of Texas at Austin
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Allan MacDonald
University of Texas at Austin, Physics, University of Texas at Austin, Department of Physics, University of Texas at Austin, Department of Physics, The University of Texas at Austin