Strange metal behavior of the Hall angle in twisted bilayer graphene

Rui Lyu, Zachary Tuchfeld, Nishchhal Verma, Haidong Tian, Kenji Watanabe, Takashi Taniguchi, Chun Ning Lau, Mohit Randeria, Marc Bockrath

Published 2020-08-16Version 1

Twisted bilayer graphene (TBG) with interlayer twist angles near the magic angle $\approx 1.08^{\circ}$ hosts flat bands and exhibits correlated states including Mott-like insulators, superconductivity and magnetism. Here we report combined temperature-dependent transport measurements of the longitudinal and Hall resistivities in close to magic-angle TBG. While the observed longitudinal resistivity follows linear temperature $T$ dependence consistent with previous reports, the Hall resistance shows an anomalous $T$ dependence with the cotangent of the Hall angle cot $\Theta{_H} \propto T^2$. Boltzmann theory for quasiparticle transport predicts that both the resistivity and cot $\Theta{_H}$ should have the same $T$ dependence, contradicting the observed behavior. This failure of quasiparticle-based theories is reminiscent of other correlated strange metals such as cuprates.