# Superconductivity, correlated insulators, and Wess–Zumino–Witten terms in twisted bilayer graphene

@article{Christos2020SuperconductivityCI, title={Superconductivity, correlated insulators, and Wess–Zumino–Witten terms in twisted bilayer graphene}, author={Maine Christos and Subir Sachdev and Mathias S. Scheurer}, journal={Proceedings of the National Academy of Sciences}, year={2020}, volume={117}, pages={29543 - 29554} }

Significance When the twist angle between two layers of graphene is close to 1.1°, the energy of an electron becomes nearly independent of its momentum, and the dominant Coulomb repulsion between the electrons leads to remarkable effects. Experiments have shown novel superconducting and insulating states. We propose here that these states are linked by a topological quantal phase, which is an analog of the Wess–Zumino–Witten term of high-energy physics. This term links spatiotemporal textures…

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## References

SHOWING 1-10 OF 62 REFERENCES

Pairing in graphenebased moiré superlattices

- (2019), arXiv:1906.03258 [cond-mat.supr-con].
- 2019

Charged skyrmions and topological origin of superconductivity in magic-angle graphene

- Physics, MedicineScience Advances
- 2021

It is shown how topological textures can mitigate Coulomb repulsion and provide a previously unexplored route to superconductivity.

Correlation-Induced Insulating Topological Phases at Charge Neutrality in Twisted Bilayer Graphene

- PhysicsPhysical Review X
- 2021

Twisted bilayer graphene (TBG) provides a unique framework to elucidate the interplay between strong correlations and topological phenomena in two-dimensional systems. The existence of multiple…

Nematicity and competing orders in superconducting magic-angle graphene

- Physics, MedicineScience
- 2021

The identification of intertwined phases with broken rotational symmetry inmagic-angle twisted bilayer graphene (TBG) is reported, indicating that nematic fluctuations might play an important role in the low-temperature phases of magic-angle TBG.

Phases of the (2+1) Dimensional SO(5) Nonlinear Sigma Model with Topological Term.

- Medicine, PhysicsPhysical review letters
- 2021

The half-filled zeroth Landau level in graphene is used as a regularization scheme to study the physics of the SO(5) nonlinear sigma model subject to a Wess-Zumino-Witten topological term in 2+1 dimensions and an ordered phase in the large U_{0} or stiff limit is observed.

Tuning electron correlation in magic-angle twisted bilayer graphene using Coulomb screening

- Medicine, PhysicsScience
- 2021

Transport measurements show that tuning Coulomb screening has opposite effects on the insulating and superconducting states: As Coulomb interaction is weakened by screening, the insulators states become less robust, whereas the stability of superconductivity at the optimal doping is enhanced.

Cascade of electronic transitions in magic-angle twisted bilayer graphene

- Medicine, PhysicsNature
- 2020

A cascade of transitions is reported that characterizes the correlated high-temperature parent phase 11, 12 from which various insulating and superconducting ground-state phases emerge at low temperatures in magic-angle twisted bilayer graphene.

Cascade of phase transitions and Dirac revivals in magic-angle graphene

- Physics, MedicineNature
- 2020

The state that is reported here, with its strongly broken electronic flavour symmetry and revived Dirac-like electronic character, is important in the physics of magic-angle graphene, forming the parent state out of which the more fragile superconducting and correlated insulating ground states emerge.

Independent superconductors and correlated insulators in twisted bilayer graphene

- Materials Science, PhysicsNature Physics
- 2020

When two sheets of graphene are stacked on top of each other with a small twist of angle θ ≈ 1.1° between them, theory predicts the formation of a flat electronic band 1 , 2 . Experiments have shown…

Microscopic pairing mechanism, order parameter, and disorder sensitivity in moiré superlattices: Applications to twisted double-bilayer graphene

- Physics
- 2020

Starting from a continuum-model description, we develop a microscopic weak-coupling theory for superconductivity in twisted double-bilayer graphene. We study both electron-phonon and entirely…