Unusual magnetotransport in twisted bilayer graphene

Abstract

Significance When two sheets of graphene are twisted to the magic angle of 1.1 ∘ , the resulting flat moiré bands can host exotic correlated electronic states such as superconductivity and ferromagnetism. Here, we show transport properties of a twisted bilayer graphene device at 1.38 ∘ , far enough above the magic angle that we do not expect exotic correlated states. Instead, we see several unusual behaviors in the device’s resistivity upon tuning both charge carrier density and perpendicular magnetic field. We can reproduce these behaviors with a surprisingly simple model based on Hofstadter’s butterfly. These results shed light on the underlying properties of twisted bilayer graphene.

Unusual magnetotransport in twisted bilayer graphene from strain-induced open Fermi surfaces

“…Finally, it predicts a Lifshitz transition from two FS pockets to one upon crossing this lower van Hove point. We reanalyze experimental data from [39], and find that these predictions are verified. The theory does not capture the electron-hole asymmetry in the experimental data.…”

“…In the weak field semiclassical regime governed by the Boltzmann equation, the open FSs generally lead to a non-saturating B 2 MR, explaining the low-field experimental findings of Ref. [39]. This theory makes a number of falsifiable predictions.…”

“…[25,50], and here it is generalized to the strained case. Since in experiments particle-hole asymmetry is evident for the off-magic-angle device [39], they would come from either higher order gradient terms beyond what's captured in the BM model in Eq. ( 2), or due to interaction effects [51][52][53][54], or their combination.…”

“…In a recent report by some of the authors [Finney et al, Ref. [39]], a TBG sample with a moiré unit cell area of 90 nm 2 (corresponding to θ = 1.38 • , well above the magic angle) displayed several unusual phenomena in magnetotransport. The sample did not exhibit the strong interaction driven effects typically observed in near-magic-angle devices.…”

“…In this work, we present a systematic theoretical study of the impact of uniaxial heterostrain on the narrow-band dispersion of TBG above the magic angle, analyze its consequences for weak field magnetotransport, and compare it with experimental data from Ref. [39]. We base our theory on the Bistritzer-MacDonald (BM) continuum model [18], incorporating heterostrain in the form of a deformation potential, a pseudo-magnetic field [40,41], and a distortion of the moiré pattern in the interlayer tunneling.…”