Anomalous Hall effect at half filling in twisted bilayer graphene

Tseng, Chun-Chih; Ma, Xuetao; Liu, Zhaoyu; Watanabe, Kenji; Taniguchi, Takashi; Chu, Jiun‐Haw; Yankowitz, Matthew

doi:10.48550/arxiv.2202.01734

Cited by 4 publications

(3 citation statements)

References 34 publications

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“…We note, that while the mean-field calculations presented here successfully capture a possible metallic AHE phase, other ground states with similar characteristics may also be possible 13,33,44,45 and are hard to rule out based on our data. Finally similar scenario to the one proposed here can also explain AHE phases observed recently near ν = ±2 46,47 .…”

supporting

confidence: 87%

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Polski¹,

Zhang²,

Yang³

et al. 2022

Preprint

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Twisted bilayer graphene (TBG) near the magic twist angle of ∼1.1°exhibits a rich phase diagram.However, the interplay between different phases and their dependence on twist angle is still elusive.Here, we explore the stability of various TBG phases and demonstrate that superconductivity near filling of two electrons per moiré unit cell alongside Fermi surface reconstructions, as well as entropydriven high-temperature phase transitions and linear-in-T resistance occur over a range of twist angles which extends far beyond those exhibiting correlated insulating phases. In the vicinity of the magic angle, we also find a metallic phase that displays a hysteretic anomalous Hall effect and incipient Chern insulating behaviour. Such a metallic phase can be rationalized in terms of the interplay between interaction-driven deformations of TBG bands leading to Berry curvature redistribution and Fermi surface reconstruction. Our results provide an extensive perspective on the hierarchy of correlated phases in TBG as classified by their robustness against deviations from the magic angle or, equivalently, their electronic interaction requirements. TBG is a highly tunable platform for exploring the effects of strong electronic interactions and topological bands [1][2][3][4][5][6][7][8][9] . At the magic angle, i.e., when the strength of the interactions among electrons is maximized relative to their kinetic energy, pronounced signatures of correlated phases emerge 1,2,10 . Away from the magic angle, the effective interaction strength is reduced and the correlated phases are believed to disappear rapidly. However, despite the strong impact of the twist angle on the phase diagram of nearly-magic TBG, this dependence is still experimentally under-explored. Here we report systematic measurements on multiple devices covering a wide range of twist angles between 0.79°and 1.23°(see Supplementary Table I for an overview) and examine the overall impact of twist angle, and thus strength of interactions, on the phase

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supporting

confidence: 87%

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Polski¹,

Zhang²,

Yang³

et al. 2022

Preprint

Self Cite

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“…Through interlayer van der Waals coupling, spatial moiré potential profoundly modifies electronic band structures, and in certain circumstances results in low energy isolated narrow or even flat bands (moiré bands) [1][2][3][4][5][6][7][8][9][10][11][12], where interactions play a vital role in low energy physics. From experimental aspect, various phases have been found in magic-angle twisted bilayer graphene (TBG), including correlated insulators [13][14][15][16][17], superconductors [13,[18][19][20], strange metal [21][22][23], magnetic phases [24][25][26][27] and quantum anomalous Hall states [28,29]. Soon after this, similar phases are also found in other forms of moiré structures including twisted double bilayer and trilayer graphene systems [30][31][32][33][34][35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

Pair-density-wave and chiral superconductivity in twisted bilayer transition-metal-dichalcogenides

Wu¹,

Wu²,

Ye³

2022

Preprint

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We theoretically explore possible unconventional superconductivity induced by weak repulsive interactions in twisted bilayer TMD (e.g. WSe2) in the presence of an out-of-plane electric field. Using renormalization group (RG) analysis, we show that topological chiral superconducting states with Chern number N = 1, 2, 4 (namely p+ip, d+id, g+ig) appear over a large parameter region with moiré filling factor around n = 1. At some special values of applied electric field and in the presence of a weak out-of-plane Zeeman field, spin-polarized pair density wave (PDW) superconductivity can emerge. This spin-polarized PDW state can be probed by experiments such as spin-polarized STM measuring spin-resolved pairing gap and quasi-particle interference. Moreover, the spin-polarized PDW could lead to spin-polarized superconducting diode effect.

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“…We should point out that our discussion has focused on the properties of the SC at ν = −2−δ, and we have deliberately avoided directing much attention to the properties of the correlated insulator (CI) at ν = −2. Assuming that the flavor polarization leading to anti-parallel SVL is present in the insulator does not uniquely fix the nature of the insulating gap, and there are various candidate orders whose competition is decided by comparatively delicate effects [39,68] (it is even possible in some samples to obtain an insulating state with a ±2e 2 /h quantized anomalous Hall effect at ν = −2 [69]). While it is natural to assume that the SC is obtained by doping holes into the CI (with this scenario apparently being born out in the STM study of [23]), this does not necessarily always need to be the case, and it is possible that different types of CIs (likely all with the same type of flavor polarization) are present in different samples that superconduct at ν = −2 − δ.…”

Section: Discussionmentioning

confidence: 99%

Pairing symmetry of twisted bilayer graphene: a phenomenological synthesis

Lake¹,

Patri²,

Senthil³

2022

Preprint

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One of the outstanding questions in the study of twisted bilayer graphene -from both experimental and theoretical points of view -is the nature of its superconducting phase. In this work we perform a comprehensive synthesis of existing experiments, and argue that experimental constraints are strong enough to allow the structure of the superconducting order parameter to be nearly uniquely determined. In particular, we argue that the order parameter is nodal, and is formed from an admixture of spin-singlet and spin-triplet Cooper pairs. This argument is made on phenomenological grounds, without committing to any particular microscopic model of the superconductor. Existing data is insufficient to determine the orbital parity of the order parameter, which could be either p-wave or d-wave. We propose a way in which the measurement of Andreev edge states can be used to distinguish between the two.

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Anomalous Hall effect at half filling in twisted bilayer graphene

Cited by 4 publications

References 34 publications

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Pair-density-wave and chiral superconductivity in twisted bilayer transition-metal-dichalcogenides

Pairing symmetry of twisted bilayer graphene: a phenomenological synthesis

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