Wide-range $T^2$ resistivity and umklapp scattering in moiré graphene

Abstract

We argue that the unusually strong electron-electron interactions in the narrow bands in moiré superlattices originate from compact Wannier orbitals. Enhanced overlaps of electronic wavefunctions, enabled by such orbitals, result in a strong el-el superlattice umklapp scattering. We identify the umklapp scattering processes as a source of the strong temperature-dependent resistivity observed in these systems. In a simple model, the umklapp scattering predicts a T -dependent resistivity that grows as T 2 and is getting bigger as the Wannier orbital radius decreases. We quantify the enhancement in el-el scattering by the Kadowaki-Woods (KW) ratio, a quantity that is sensitive to umklapp scattering but, helpfully, insensitive to the effects due to the high density of electronic states. Our analysis predicts anomalously large KW ratio values that clearly indicate the importance of the umklapp el-el processes and their impact on the T -dependent resistivity.

Strange metallicity of moiré twisted bilayer graphene

“…In fact, we believe that any umklapp electron-electron interaction is likely to produce a T 2 low-temperature resistivity in tBLG itself as has recently been argued in the literature. [31,32] Thus, the appearance of a linear-in-T resistivity in tBLG down to arbitrarily low temperatures for some specific band fillings, as reported in Ref. 1 (and earlier in Ref.…”