Details

Autor(en) / Beteiligte

• Lu, Xiaobo
• Stepanov, Petr
• Yang, Wei
• Xie, Ming
• Aamir, Mohammed Ali
• Das, Ipsita
• Urgell, Carles
• Watanabe, Kenji
• Taniguchi, Takashi
• Zhang, Guangyu
• Bachtold, Adrian
• MacDonald, Allan H
• Efetov, Dmitri K

Titel

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

Ist Teil von

• Nature (London), 2019-10, Vol.574 (7780), p.653-657

Ort / Verlag

England: Nature Publishing Group

Erscheinungsjahr

2019

Link zum Volltext

Beschreibungen/Notizen

• Superconductivity can occur under conditions approaching broken-symmetry parent states . 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 physics , notably superconductivity, which emerges close to interaction-induced insulating states . Here we report the fabrication of magic-angle twisted bilayer graphene devices with highly uniform twist angles. The reduction in twist-angle disorder reveals the presence of insulating states at all integer occupancies of the fourfold spin-valley degenerate flat conduction and valence bands-that is, at moiré band filling factors ν = 0, ±1, ±2, ±3. At ν ≈ -2, superconductivity is observed below critical temperatures of up to 3 kelvin. We also observe three new superconducting domes at much lower temperatures, close to the ν = 0 and ν = ±1 insulating states. Notably, at ν = ± 1 we find states with non-zero Chern numbers. For ν = -1 the insulating state exhibits a sharp hysteretic resistance enhancement when a perpendicular magnetic field greater than 3.6 tesla is applied, which is consistent with a field-driven phase transition. Our study shows that broken-symmetry states, interaction-driven insulators, orbital magnets, states with non-zero Chern numbers and superconducting domes occur frequently across a wide range of moiré flat band fillings, including close to charge neutrality. This study provides a more detailed view of the phenomenology of magic-angle twisted bilayer graphene, adding to our evolving understanding of its emergent properties.