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Quantum critical behaviour in magic-angle twisted bilayer graphene

Abstract

The flat bands1 of magic-angle twisted bilayer graphene (MATBG) host strongly correlated electronic phases such as correlated insulators2,3,4,5,6, superconductors7,8,9,10,11 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.

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Fig. 1: Temperature dependence of the resistivity of hole-doped MATBG.
Fig. 2: Phase diagram of hole-doped screened MATBG.
Fig. 3: Magnetic field dependence of the resistivity of hole-doped MATBG.

Data availability

Source data are provided with this paper. All other datasets that support the plots within this publication are available from the corresponding authors upon reasonable request.

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Acknowledgements

We are grateful for fruitful discussions with A. MacDonald, P. Jarillo-Herrero and P. Coleman. D.K.E. acknowledges support from the Ministry of Economy and Competitiveness of Spain through the ‘Severo Ochoa’ programme for Centres of Excellence in R&D (SE5-0522), Fundació Privada Cellex, Fundació Privada Mir-Puig, the Generalitat de Catalunya through the CERCA programme and funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 852927). J.D.-M. acknowledges support from the INphINIT ‘la Caixa’ Foundation (ID 100010434) fellowship programme (LCF/BQ/DI19/11730021). G.D.B. acknowledges funding from the ‘Presidencia de la Agencia Estatal de Investigación’ within the ‘Convocatoria de tramitación anticipada, correspondiente al año 2019, de las ayudas para contratos predoctorales (Ref. PRE2019-088487) para la formación de doctores contemplada en el Subprograma Estatal de Formación del Programa Estatal de Promoción del Talento y su Empleabilidad en I+D+i, en el marco del Plan Estatal de Investigación Científica y Técnica y de Innovación 2017-2020, cofinanciado por el Fondo Social Europeo’. I.D. acknowledges support from the INphINIT ‘La Caixa’ (ID 100010434) fellowship programme (LCF/BQ/DI19/11730030). K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan (grant number JPMXP0112101001) and JSPS KAKENHI (grant numbers 19H05790 and JP20H00354). L.L. acknowledges support from the Science and Technology Center for Integrated Quantum Materials, NSF Grant No. DMR-1231319 and Army Research Office Grant W911NF-18-1-0116.

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Authors and Affiliations

Authors

Contributions

D.K.E. and X.L. conceived and designed the experiments. I.D., G.D.B., J.D.-M. and X.L. fabricated the devices. A.J., I.D., G.D.B., J.D.-M. and X.L. performed the measurements. A.J. analysed the data. A.J., H.I. and L.L. performed the theoretical modelling. T.T. and K.W. contributed materials. D.K.E. supported the experiments. A.J. and D.K.E. wrote the paper.

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Correspondence to Alexandre Jaoui or Dmitri K. Efetov.

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Supplementary Information

Supplementary Notes A–J, Figs. 1–8 and Table 1.

Source data

Source Data Fig. 1

Numerical source data for Fig. 1.

Source Data Fig. 2

Numerical source data for Fig. 2.

Source Data Fig. 3

Numerical source data for Fig. 3.

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Jaoui, A., Das, I., Di Battista, G. et al. Quantum critical behaviour in magic-angle twisted bilayer graphene. Nat. Phys. 18, 633–638 (2022). https://doi.org/10.1038/s41567-022-01556-5

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