Phonon scattering dominated electron transport in twisted bilayer graphene

Abstract

Twisted bilayer graphene (tBLG) has recently emerged as a platform for hosting correlated phenomena, owing to the exceptionally flat band dispersion that results near interlayer twist angle $θ\approx1.1^\circ$. At low temperature a variety of phases are observed that appear to be driven by electron interactions including insulating states, superconductivity, and magnetism. Electrical transport in the high temperature regime has received less attention but is also highly anomalous, exhibiting gigantic resistance enhancement and non-monotonic temperature dependence. Here we report on the evolution of the scattering mechanisms in tBLG over a wide range of temperature and for twist angle varying from 0.75$^\circ$ - 2$^\circ$. We find that the resistivity, $ρ$, exhibits three distinct phenomenological regimes as a function of temperature, $T$. At low $T$ the response is dominated by correlation and disorder physics; at high $T$ by thermal activation to higher moiré subbands; and at intermediate temperatures $ρ$ varies linearly with $T$. The $T$-linear response is much larger than in monolayer graphenefor all measured twist angles, and increases by more than three orders of magnitude for $θ$ near the flat-band condition. Our results point to the dominant role of electron-phonon scattering in twisted layer systems, with possible implications for the origin of the observed superconductivity.