Strange metal behavior of the Hall angle in twisted bilayer graphene

Twisted bilayer graphene (TBG) with interlayer twist angles near the magic angle approximate to 1.08 degrees hosts flat bands and exhibits correlated states including Mott-like insulators, superconductivity, and magnetism. A linear-intemperature normal state resistivity in TBG has been attributed to an exotic Planckian dissipation mechanism but can be equally well explained in terms of conventional electron-phonon scattering. To address this issue, we perform combined temperature-dependent transport measurements of both the longitudinal and Hall resistivities in near-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) proportional to 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.

Automated summary

Twisted bilayer graphene (TBG) near the magic angle with flat bands exhibits correlated states including Mott-like insulators, superconductivity, and magnetism. The linear temperature-dependent normal state resistivity in TBG can be attributed to both an exotic Planckian dissipation mechanism and conventional electron-phonon scattering. However, the observed anomalous temperature dependence of longitudinal and Hall resistivities in near-magic-angle TBG contradicts predictions based on quasiparticle transport theory.