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Studying strong electronic correlations has been an essential driving force pushing the frontiers of condensed matter physics. In particular, in the vicinity of correlation-driven quantum phase transitions, quantum critical fluctuations of multiple degrees of freedom facilitate exotic many-body states beyond Landau’s framework. Hence, engineering the interplay of these degrees of freedom is of particular importance to reveal various quantum critical phases and excitation therein. Recently, moiré heterostructures of van der Waals materials have been demonstrated as a highly tunable quantum platform for a number of correlated quantum phases. Here, by continuously varying the displacement field and parallel magnetic field, we observe tunable quantum melting of the generalized Wigner crystal state with spin and valley isospins arising in chiral-stacked twisted double bilayer graphene (cTDBG). The quantum critical regime manifests itself as a strange metal phase, indicating breakdown of Landau’s quasiparticle excitations. Moreover, scaling analysis shows that quantum melting of the generalized Wigner crystal to a Fermi liquid undergoes two distinct continuous quantum phase transitions, suggesting the existence of an intermediate ground state. The intermediate strange metal phase and ground state, as well as the quantum criticality, can be tuned by applying a parallel magnetic field, revealing an intricate interplay between the strong electronic correlations and isospin degrees of freedom. Our findings reveal a new solid-state simulator with the interplay of multiple degrees of freedom for the extended Hubbard model.

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• Creative Commons BY Attribution 4.0 International
  

Keyword: Quantum criticality, Hubbard model, twisted double bilayer graphene

Date published: 2022-09-15

Publisher: Springer Science and Business Media LLC

Journal:

• Nature (ISSN: 00280836) vol. 609 issue. 7927 p. 479-484

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Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1038/s41586-022-05106-0

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Updated at: 2025-03-01 12:30:20 +0900

Published on MDR: 2025-03-01 12:30:20 +0900