Quantum critical behaviour in magic-angle twisted bilayer graphene

By Alexandre Jaoui, Ipsita Das, G. Di Battista, J. Díez-Mérida, Xiaobo Lu, Kenji Watanabe, Takashi Taniguchi, H. Ishizuka, L. Levitov, D. Efetov. Nature Physics, 2021

173 citations recorded by the source corpus.

The flat bands1 of magic-angle twisted bilayer graphene (MATBG) host strongly correlated electronic phases such as correlated insulators2–6, superconductors7–11 and a strange metal state12. The strange metal state, believed to be key for understanding the electronic properties of MATBG, is obscured by various phase transitions and so it could not be unequivocally differentiated from a metal undergoing frequent electron–phonon collisions13. Here we report transport measurements in superconducting MATBG in which the correlated insulator states are suppressed by screening. The uninterrupted metallic ground state shows resistivity that is linear in temperature over three orders of magnitude and spans a broad range of doping, including that where a correlation-driven Fermi surface reconstruction occurs. This strange metal behaviour is distinguished by Planckian scattering rates and a linear magnetoresistivity. By contrast, near charge neutrality or a fully filled flat band, as well as for devices twisted away from the magic angle, we observe the archetypal Fermi-liquid behaviour. Our measurements demonstrate the existence of a quantum-critical phase whose fluctuations dominate the metallic ground state throughout a continuum of doping. Further, we observe a transition to the strange metal upon suppression of the superconducting order, suggesting a relationship between quantum fluctuations and superconductivity in MATBG. The presence or absence of a strange metal phase in twisted bilayer graphene has been controversial. Now, measurements over a wide range of temperature and doping give much stronger evidence for its existence.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/8def0381f0a8532d052c16f96cda2c32a173cdb3

Citations in the corpus

• Flat bands, strange metals and the Kondo effect (2023, unknown): “Interestingly, by bringing a screening layer in close vicinity to the twisted bilayers, this insulating state is quenched and a strange metal results 90 .”