Superconductors, orbital magnets and correlated states in magic-angle bilayer graphene

@article{Lu2019SuperconductorsOM,
  title={Superconductors, orbital magnets and correlated states in magic-angle bilayer graphene},
  author={Xiaobo Lu and Petr Stepanov and Wei Yang and Ming Xie and Mohammed Ali Aamir and Ipsita Das and C. Urgell and Kenji Watanabe and Takashi Taniguchi and Guangyu Zhang and Adrian Bachtold and Allan H Macdonald and Dmitri K. Efetov},
  journal={Nature},
  year={2019},
  volume={574},
  pages={653-657}
}
Superconductivity can occur under conditions approaching broken-symmetry parent states1. In bilayer graphene, the twisting of one layer with respect to the other at ‘magic’ twist angles of around 1 degree leads to the emergence of ultra-flat moiré superlattice minibands. Such bands are a rich and highly tunable source of strong-correlation physics2–5, notably superconductivity, which emerges close to interaction-induced insulating states6,7. Here we report the fabrication of magic-angle twisted… 

Superconductivity in metallic twisted bilayer graphene stabilized by WSe2

It is shown that adding an insulating tungsten diselenide monolayer between the hBN and the TBG stabilizes superconductivity at twist angles much smaller than the magic angle, constrain theoretical explanations for the emergence ofsuperconductivity in TBG and open up avenues towards engineering quantum phases in moiré systems.

Robust superconductivity in magic-angle multilayer graphene family

The discovery of correlated states and superconductivity in magic-angle twisted bilayer graphene (MATBG) established a new platform to explore interaction-driven and topological phenomena. However,

Orderly disorder in magic-angle twisted trilayer graphene

Magic-angle twisted trilayer graphene (TTG) has recently emerged as a platform to engineer strongly correlated flat bands. We reveal the normal-state structural and electronic properties of TTG using

Superconductivity without insulating states in twisted bilayer graphene stabilized by monolayer WSe$_2$

Magic-angle twisted bilayer graphene (TBG), with rotational misalignment close to 1.1∘, features isolated flat electronic bands that host a rich phase diagram of correlated insulating,

Nature of the Correlated Insulator States in Twisted Bilayer Graphene.

It is found that gaps between the flat conduction and valence bands open at neutrality over a wide range of twist angles, sometimes without breaking the system's valley projected C_{2}T symmetry.

Tunable strongly coupled superconductivity in magic-angle twisted trilayer graphene.

It is found that the superconducting phase is suppressed and bounded at the Van Hove singularities that partially surround the broken-symmetry phase, which is difficult to reconcile with weak-coupling Bardeen-Cooper-Schrieffer theory.

Independent superconductors and correlated insulators in twisted bilayer graphene

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

Emergence of Chern Insulating States in Non-Magic Angle Twisted Bilayer Graphene

Twisting two layers into a magic angle (MA) of ∼1.1° is found essential to create low energy flat bands and the resulting correlated insulating, superconducting, and magnetic phases in twisted

Nematic superconductivity in magic-angle twisted bilayer graphene from atomistic modeling

Twisted bilayer graphene (TBG) develops large moiré patterns at small twist angles with flat energy bands hosting domes of superconductivity. The large system size and intricate band structure have

Graphene bilayers with a twist

This Review highlights some key research results in this field, point to important questions that remain open and comment on the place of magic-angle twisted bilayer graphene in the strongly correlated quantum matter world.
...

References

SHOWING 1-10 OF 50 REFERENCES

Unconventional superconductivity in magic-angle graphene superlattices

The realization of intrinsic unconventional superconductivity is reported—which cannot be explained by weak electron–phonon interactions—in a two-dimensional superlattice created by stacking two sheets of graphene that are twisted relative to each other by a small angle.

Nature of the Correlated Insulator States in Twisted Bilayer Graphene.

It is found that gaps between the flat conduction and valence bands open at neutrality over a wide range of twist angles, sometimes without breaking the system's valley projected C_{2}T symmetry.

Tuning superconductivity in twisted bilayer graphene

This study demonstrates twisted bilayer graphene to be a distinctively tunable platform for exploring correlated states by inducing superconductivity at a twist angle larger than 1.1°—in which correlated phases are otherwise absent—by varying the interlayer spacing with hydrostatic pressure.

Possible correlated insulating states in magic-angle twisted bilayer graphene under strongly competing interactions

We investigate correlated insulating states in magic-angle twisted bilayer graphene (TBG) by the exact diagonalization method applied to the extended Hubbard model with interaction parameters

Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene

Evidence is presented that near three-quarters of the filling of the conduction miniband, these enhanced interactions drive the twisted bilayer graphene into a ferromagnetic state, and measurements suggest that the system may be an incipient Chern insulator.

Signatures of tunable superconductivity in a trilayer graphene moiré superlattice

This study shows that ABC-TLG/hBN heterostructures offer attractive model systems in which to explore rich correlated behaviour emerging in the tunable triangular Hubbard model by varying the vertical displacement field in a trilayer graphene and hexagonal boron nitride moiré superlattice.

Strange Metal in Magic-Angle Graphene with near Planckian Dissipation.

This work shows that magic-angle bilayer graphene exhibits another hallmark of strongly correlated systems-a broad regime of T-linear resistivity above a small density-dependent crossover temperature-for a range of fillings near the correlated insulator.

Origin of Magic Angles in Twisted Bilayer Graphene.

A fundamental continuum model for TBG is reported which features not just the vanishing of the Fermi velocity, but also the perfect flattening of the entire lowest band.

Twisted Bilayer Graphene: A Phonon-Driven Superconductor.

It is shown that phonon-mediated electron attraction at the magic angle is strong enough to induce a conventional intervalley pairing between graphene valleys K and K^{'} with a superconducting critical temperature T_{c}∼1  K, in agreement with the experiment.

Phonon-induced giant linear-in- T resistivity in magic angle twisted bilayer graphene: Ordinary strangeness and exotic superconductivity

We theoretically show that twisted bilayer graphene should have an enhanced linear-in-temperature resistivity in the metallic regime with the resistivity magnitude increasing as the twist angle