Ground State and Hidden Symmetry of Magic-Angle Graphene at Even Integer Filling
By Nick Bultinck, E. Khalaf, Shang Liu, S. Chatterjee, Ashvin Vishwanath, M. Zaletel. 2019
296 citations recorded by the source corpus.
In magic angle twisted bilayer graphene, electron-electron interactions play a central role resulting in correlated insulating states at certain integer fillings. Identifying the nature of these insulators is a central question and potentially linked to the relatively high temperature superconductivity observed in the same devices. Here we address this question using a combination of analytical strong-coupling arguments and a comprehensive Hartree-Fock numerical calculation which includes the effect of remote bands. The ground state we obtain at charge neutrality is an unusual ordered state which we call the Kramers intervalley-coherent (K-IVC) insulator. In its simplest form, the K-IVC exhibits a pattern of alternating circulating currents which triples the graphene unit cell leading to an "orbital magnetization density wave". Although translation and time reversal symmetry are broken, a combined `Kramers' time reversal symmetry is preserved. Our analytic arguments are built on first identifying an approximate ${\rm U}(4) \times {\rm U}(4)$ symmetry, resulting from the remarkable properties of the tBG band structure, which helps select a low energy manifold of states, which are further split to favor the K-IVC. This low energy manifold is also found in the Hartree-Fock numerical calculation. We show that symmetry lowering perturbations can stabilize other insulators and the semi-metallic state, and discuss the ground state at half filling and a comparison with experiments.
Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry
View Paper: https://www.semanticscholar.org/paper/9bedc60fdfce8b5df699811f50681dc0a96bef99
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In Atomic and Molecular Physics, and Optics
In Materials Chemistry
Citations in the corpus
- Spontaneous fractional Chern insulators in transition metal dichalcogenide moiré superlattices (2021, background): “[66] Nick Bultinck, Eslam Khalaf, Shang Liu, Shubhayu Chatterjee, Ashvin Vishwanath, and Michael P.”
- Flat bands, strange metals and the Kondo effect (2023, unknown): “1.”
- Superconductivity, superfluidity and quantum geometry in twisted multilayer systems (2021, background): “The correlated insulator phases can be understood as ferromagnets of this large symmetry group [79, 80, 93, 102].”