Strange metal behavior of the Hall angle in twisted bilayer graphene

TL;DR

This study reveals that twisted bilayer graphene near the magic angle exhibits strange metal behavior, with a linear temperature dependence of resistivity and an anomalous quadratic temperature dependence of the Hall angle cotangent, challenging quasiparticle theories.

Contribution

The paper provides experimental evidence of strange metal behavior in twisted bilayer graphene, highlighting deviations from conventional quasiparticle transport theories.

Findings

Longitudinal resistivity shows linear T dependence.

Hall angle cotangent varies as T^2, contrary to quasiparticle predictions.

Quasiparticle theories fail to explain observed transport behavior.

Abstract

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.