Theory of correlated insulators and superconductivity in twisted bilayer graphene

Shavit, Gal; Berg, Erez; Stern, Ady; Oreg, Yuval

doi:10.48550/arxiv.2107.08486

Cited by 3 publications

(3 citation statements)

References 59 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Due the metallic nature of the system, the Streda formula with C = −1; ν = 1 at B = 0 T is only approximately satisfied. 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 .…”

mentioning

confidence: 61%

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Polski¹,

Zhang²,

Yang³

et al. 2022

Preprint

View full text Add to dashboard Cite

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

show abstract

mentioning

confidence: 61%

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Polski¹,

Zhang²,

Yang³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…Combined, these observations suggest that superconductivity is favoured when only two out of the four flavours are significantly populated (|ν| = 2 cascade) and suppressed beyond |ν| = 3 resets. This behaviour can be understood within the simplest iteration of the cascade scenario: resets at |ν| = 3 produce spin-and valley-polarized bands [21][22][23] and naturally disfavour Cooper pairing of time-reversed partners.…”

mentioning

confidence: 99%

Ascendance of Superconductivity in Magic-Angle Graphene Multilayers

Zhang¹,

Polski²,

Lewandowski³

et al. 2021

Preprint

View full text Add to dashboard Cite

“…Indeed we believe that this is one of the few cases where such a choice impacts a physical quantity in a qualitative way. Many theoretical studies focus primarily on the type of symmetry-breaking order 5,6,8,20,64,65,[74][75][76][77][78][79][80][81][82][83] -all the schemes studied here lead to the KIVC which only requires that J, λ > 0. On the other hand, we are interested in the θ-dependence of E c which depends sensitively on the value of J itself.…”

Section: Effective Mass Of Paired Skyrmionsmentioning

confidence: 99%

Skyrmions in twisted bilayer graphene: stability, pairing, and crystallization

Kwan¹,

Wagner²,

Bultinck³

et al. 2021

Preprint

View full text Add to dashboard Cite

We study the excitations that emerge upon doping the translationally-invariant correlated insulating states in magic angle twisted bilayer graphene at various integer filling factors ν. We identify parameter regimes where these are associated with skyrmion textures in the spin or pseudospin degrees of freedom, and explore both short-distance pairing effects and the formation of long-range ordered skyrmion crystals. We perform a comprehensive analysis of the pseudospin skyrmions that emerge upon doping insulators at even ν, delineating the regime in parameter space where these are the lowest-energy charged excitations by means of self-consistent Hartree-Fock calculations on the interacting Bistritzer-MacDonald model. We explicitly demonstrate the purely electron-mediated pairing of skyrmions, a key ingredient behind a recent proposal of skyrmion superconductivity. Building upon this, we construct hopping models to extract the effective masses of paired skyrmions, and discuss our findings and their implications for skyrmion superconductivity in relation to experiments, focusing on the dome-shaped dependence of the transition temperature on the twist angle. We also investigate the properties of spin skyrmions about the quantized anomalous Hall insulator at ν = +3. In both cases, we demonstrate the formation of robust spin/pseudospin skyrmion crystals upon doping to a finite density away from integer filling.

show abstract

Theory of correlated insulators and superconductivity in twisted bilayer graphene

Cited by 3 publications

References 59 publications

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Ascendance of Superconductivity in Magic-Angle Graphene Multilayers

Skyrmions in twisted bilayer graphene: stability, pairing, and crystallization

Contact Info

Product

Resources

About