Tunable quantum criticalities in an isospin extended Hubbard model simulator

Qiao Li, Bin Cheng (), Moyu Chen, Bo Xie, Yongqin Xie, Pengfei Wang, Fanqiang Chen, Zenglin Liu, Kenji Watanabe, Takashi Taniguchi, Shi-Jun Liang, Da Wang, Chenjie Wang, Qiang-Hua Wang, Jianpeng Liu and Feng Miao ()
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Qiao Li: Nanjing University
Bin Cheng: Nanjing University of Science and Technology
Moyu Chen: Nanjing University
Bo Xie: ShanghaiTech University
Yongqin Xie: Nanjing University
Pengfei Wang: Nanjing University
Fanqiang Chen: Nanjing University
Zenglin Liu: Nanjing University
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Shi-Jun Liang: Nanjing University
Da Wang: Nanjing University
Chenjie Wang: The University of Hong Kong
Qiang-Hua Wang: Nanjing University
Jianpeng Liu: ShanghaiTech University
Feng Miao: Nanjing University

Nature, 2022, vol. 609, issue 7927, 479-484

Abstract: Abstract Studying strong electron correlations has been an essential driving force for pushing the frontiers of condensed matter physics. In particular, in the vicinity of correlation-driven quantum phase transitions (QPTs), quantum critical fluctuations of multiple degrees of freedom facilitate exotic many-body states and quantum critical behaviours beyond Landau’s framework1. Recently, moiré heterostructures of van der Waals materials have been demonstrated as highly tunable quantum platforms for exploring fascinating, strongly correlated quantum physics2–22. Here we report the observation of tunable quantum criticalities in an experimental simulator of the extended Hubbard model with spin–valley isospins arising in chiral-stacked twisted double bilayer graphene (cTDBG). Scaling analysis shows a quantum two-stage criticality manifesting two distinct quantum critical points as the generalized Wigner crystal transits to a Fermi liquid by varying the displacement field, suggesting the emergence of a critical intermediate phase. The quantum two-stage criticality evolves into a quantum pseudo criticality as a high parallel magnetic field is applied. In such a pseudo criticality, we find that the quantum critical scaling is only valid above a critical temperature, indicating a weak first-order QPT therein. Our results demonstrate a highly tunable solid-state simulator with intricate interplay of multiple degrees of freedom for exploring exotic quantum critical states and behaviours.

Date: 2022
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DOI: 10.1038/s41586-022-05106-0

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