Abstract
Understanding the normal-metal state transport in twisted bilayer graphene near magic angle is of fundamental importance as it provides insights into the mechanisms responsible for the observed strongly correlated insulating and superconducting phases. Here we provide a rigorous theory for phonon-dominated transport in twisted bilayer graphene describing its unusual signatures in the resistivity (including the variation with electron density, temperature, and twist angle) showing good quantitative agreement with recent experiments. We contrast this with the alternative Planckian dissipation mechanism that we show is incompatible with available experimental data. An accurate treatment of the electron-phonon scattering requires us to go well beyond the usual treatment, including both intraband and interband processes, considering the finite-temperature dynamical screening of the electron-phonon matrix element, and going beyond the linear Dirac dispersion. In addition to explaining the observations in currently available experimental data, we make concrete predictions that can be tested in ongoing experiments.
Highlights
Understanding the normal-metal state transport in twisted bilayer graphene near magic angle is of fundamental importance as it provides insights into the mechanisms responsible for the observed strongly correlated insulating and superconducting phases
Fermi velocity at low energy and a reduction of the bandwidth of the lowest energy band. Both these effects enhance the importance of electron–electron interactions[7]. These properties can be understood as follows: In the absence of any coupling between the layers, the original Dirac-like bands are just folded onto the smaller moiré Brillouin zone as determined by symmetry, but not modified; it is the interlayer coupling that causes level repulsion between the folded moiré bands
The moiré band closest to charge neutrality remains Dirac-like at low energy but with a reduced Fermi velocity, and the first moiré band as a whole gets squeezed by the level repulsion
Summary
Understanding the normal-metal state transport in twisted bilayer graphene near magic angle is of fundamental importance as it provides insights into the mechanisms responsible for the observed strongly correlated insulating and superconducting phases. By considering the finite-temperature dynamical screening of the electron–phonon matrix element, we show, for example, that only the antisymmetric gauge phonon mode survives at a low twist angle; and by going beyond the linear Dirac dispersion, we show that the van Hove singularity causes saturation in resistivity as a function of temperature.
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