Observation of Reentrant Correlated Insulators and Interaction-Driven Fermi-Surface Reconstructions at One Magnetic Flux Quantum per Moiré Unit Cell in Magic-Angle Twisted Bilayer Graphene

Das, Ipsita; Shen, Cheng; Jaoui, Alexandre; Herzog-Arbeitman, Jonah; Chew, Aaron; Cho, Chang-Woo; Watanabe, Kenji; Taniguchi, Takashi; Piot, B. A.; Bernevig, B. Andrei; Efetov, Dmitri K.

doi:10.1103/physrevlett.128.217701

Cited by 26 publications

(5 citation statements)

References 33 publications

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“…Twisted bilayer graphene (TBG) system around the magic angle is an ideal platform to realize various intriguing quantum phases , such as the correlated insulators, − quantum anomalous Hall states, and ,,− unconventional superconductivity. ,− ,,− Around magic angle 1.05°, there are two topologically nontrivial flat bands contributed by each valley and spin degrees of freedom. − A lot of the unusual phenomena, including correlated insulators and quantum anomalous Hall effects, can be attributed to the presence of such topologically nontrivial flat bands in the electronic degrees of freedom. The electron–electron (e–e) Coulomb interactions dominates over the kinetic energy near magic angle, and the interplay between the strong Coulomb correlations and the nontrivial topology of the flat bands give rise to diverse correlated insulator states and topological states, which have been extensively studied from the theoretical point of view over the past few years. − …”

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confidence: 99%

Moiré Phonons in Magic-Angle Twisted Bilayer Graphene

et al. 2022

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Magic-angle twisted bilayer graphene (TBG) has attracted significant interest recently due to the discoveries of diverse correlated and topological states. In this work, we study the phonon properties in magic-angle TBG based on many-body classical potential and interatomic forces generated by a deep neural network trained with data from ab initio calculations. We have discovered a number of soft modes which can exhibit dipolar, quadrupolar, and octupolar vibrational patterns in real space, as well as some time-reversal breaking chiral phonon modes. We have further studied the phonon effects on the electronic structures by freezing certain soft phonon modes. We find that if a soft quadrupolar phonon mode is assumed to be frozen, the system would exhibit a charge order which is perfectly consistent with recent experiments. Moreover, once some lowfrequency C 2z -breaking modes get frozen, the Dirac points at the charge neutrality point would be gapped out, which provides an alternative perspective to the origin of correlated insulator state at charge neutrality point.

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confidence: 99%

Moiré Phonons in Magic-Angle Twisted Bilayer Graphene

et al. 2022

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“…The effect of renormalization of mean field parameters in magnetic field and heterostrain is yet to be incorporated in our framework. A full analysis for other integer fillings, translation symmetry broken candidate ground states and Hofstadter-scale fluxes where reentrant many-body and topological effects are at play 52 , 66 – 68 , is also left for the future work.…”

Section: Discussionmentioning

confidence: 99%

“…The large moiré period of ~13 nm in MATBG has revealed a sequence of broken symmetry Chern insulators yielding a plethora of finite magnetic field (B) induced phases at lower fluxes 42,[44][45][46][47][48][49][50][51] and has showcased, for the first time, reentrant correlated Hofstadter states at magnetic fields as low as 31T 52 . Thus it becomes important to better understand the interplay of correlations and band topology in the presence of a perpendicular B field.…”

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Topological heavy fermions in magnetic field

Singh,

Chew,

Herzog-Arbeitman

et al. 2024

Nat Commun

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The recently introduced topological heavy fermion model (THFM) provides a means for interpreting the low-energy electronic degrees of freedom of the magic angle twisted bilayer graphene as hybridization amidst highly dispersing topological conduction and weakly dispersing localized heavy fermions. In order to understand the Landau quantization of the ensuing electronic spectrum, a generalization of THFM to include the magnetic field B is desired, but currently missing. Here we provide a systematic derivation of the THFM in B and solve the resulting model to obtain the interacting Hofstadter spectra for single particle charged excitations. While naive minimal substitution within THFM fails to correctly account for the total number of magnetic subbands within the narrow band i.e., its total Chern number, our method—based on projecting the light and heavy fermions onto the irreducible representations of the magnetic translation group— reproduces the correct total Chern number. Analytical results presented here offer an intuitive understanding of the nature of the (strongly interacting) Hofstadter bands.

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“…However, the single particle bandstructure in the non-interacting regime suggests Hofstadter subbands at high−B in MATBG, which was previously unexplored. Recently, Das et al [212] studied the magnetotransport in MATBG upto B = 31 T which produces one magnetic flux quantum per moiré unit cell. In addition to Hofstadter butterfly, they also found a re-entrant correlated insulator at half filling ν = +2 (figure 11(b)).…”

Section: Unconventional Quantum Hall Phasesmentioning

confidence: 99%

Emergent phases in graphene flat bands

Bhowmik,

Ghosh,

Chandni

2024

Rep. Prog. Phys.

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Electronic correlations in two-dimensional materials play a crucial role in stabilising emergent phases of matter. The realisation of correlation-driven phenomena in graphene has remained a longstanding goal, primarily due to the absence of strong electron-electron interactions within its low-energy bands. In this context, magic-angle twisted bilayer graphene has recently emerged as a novel platform featuring correlated phases favoured by the low-energy flat bands of the underlying moiré superlattice. Notably, the observation of correlated insulators and superconductivity has garnered significant attention, leading to substantial progress in theoretical and experimental studies aiming to elucidate the origin and interplay between these two phases. A wealth of correlated phases with unprecedented tunability was discovered subsequently, including orbital ferromagnetism, Chern insulators, strange metallicity, density waves, and nematicity. However, a comprehensive understanding of these closely competing phases remains elusive. The ability to controllably twist and stack multiple graphene layers has enabled the creation of a whole new family of moiré superlattices with myriad properties being discovered at a fast pace. Here, we review the progress and development achieved so far, encompassing the rich phase diagrams offered by these graphene-based moiré systems. Additionally, we discuss multiple phases recently observed in non-moiré multilayer graphene systems. Finally, we outline future opportunities and challenges for the exploration of hidden phases in this new generation of moiré materials.

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Observation of Reentrant Correlated Insulators and Interaction-Driven Fermi-Surface Reconstructions at One Magnetic Flux Quantum per Moiré Unit Cell in Magic-Angle Twisted Bilayer Graphene

Cited by 26 publications

References 33 publications

Moiré Phonons in Magic-Angle Twisted Bilayer Graphene

Moiré Phonons in Magic-Angle Twisted Bilayer Graphene

Topological heavy fermions in magnetic field

Emergent phases in graphene flat bands

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