Helical trilayer graphene: a moiré platform for strongly-interacting topological bands

Abstract

Quantum geometry of electronic wavefunctions results in fascinating topological phenomena. A prominent example is the intrinsic anomalous Hall effect (AHE) in which a Hall voltage arises in the absence of an applied magnetic field. The AHE requires a coexistence of Berry curvature and spontaneous time-reversal symmetry breaking. These conditions can be realized in two-dimensional moiré systems with broken $xy$-inversion symmetry ($C_{2z}$) that host flat electronic bands. Here, we explore helical trilayer graphene (HTG), three graphene layers twisted sequentially by the same angle forming two misoriented moiré patterns. Although HTG is globally $C_{2z}$-symmetric, surprisingly we observe clear signatures of topological bands. At a magic angle ${\theta }_{\mathrm{m}}\approx 1.8^{\circ }$, we uncover a robust phase diagram of correlated and magnetic states using magnetotransport measurements. Lattice relaxation leads to large periodic domains in which $C_{2z}$ is broken on the moiré scale. Each domain harbors flat topological bands with valley-contrasting Chern numbers $\pm (1,-2)$. We find correlated states at integer electron fillings per moiré unit cell $\nu =1,2,3$ and fractional fillings $2/3,7/2$ with the AHE arising at $\nu =1,3$ and $2/3,7/2$. At $\nu =1$, a time-reversal symmetric phase appears beyond a critical electric displacement field, indicating a topological phase transition. Finally, hysteresis upon sweeping $\nu$ points to first-order phase transitions across a spatial mosaic of Chern domains separated by a network of topological gapless edge states. We establish HTG as an important platform that realizes ideal conditions for exploring strongly interacting topological phases and, due to its emergent moiré-scale symmetries, demonstrates a novel way to engineer topology.

References in corpus (19)

• Tunable Phase Boundaries and Ultra-Strong Coupling Superconductivity in Mirror Symmetric Magic-Angle Trilayer Graphene
• Signatures of Fractional Quantum Anomalous Hall States in Twisted MoTe2 Bilayer
• Observation of Fractionally Quantized Anomalous Hall Effect
• Integer and fractional Chern insulators in twisted bilayer MoTe2
• Superconductivity and strong interactions in a tunable moiré quasiperiodic crystal
• Programming Correlated Magnetic States via Gate Controlled Moiré Geometry
• Interlayer interaction in general incommensurate atomic layers
• Flat bands and perfect metal in trilayer moiré graphene
• Mapping twist-tuned multiband topology in bilayer WSe${}_2$
• Magic-angle helical trilayer graphene
• Exact Many-Body Ground States from Decomposition of Ideal Higher Chern Bands: Applications to Chirally Twisted Graphene Multilayers
• Spontaneous time-reversal symmetry breaking in twisted double bilayer graphene
• Supermoiré low-energy effective theory of twisted trilayer graphene
• Angle-resolved transport nonreciprocity and spontaneous symmetry breaking in twisted trilayer graphene
• Evolution of Superconductivity in Twisted Graphene Multilayers
• Local spectroscopy of a gate-switchable moiré quantum anomalous Hall insulator
• Extended magic phase in twisted graphene multilayers
• Non-coplanar magnetism, topological density wave order and emergent symmetry at half-integer filling of moiré Chern bands
• Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Cited by in corpus (13)

• Magnetic Bloch States at Integer Flux Quanta Induced by Super-moiré Potential in Graphene Aligned with Twisted Boron Nitride
• Chern-Textured Exciton Insulators with Valley Spiral Order in Moiré Materials
• Quantum anomalous Hall effects and emergent $\mathrm{SU}(2)$ Hall ferromagnets at fractional filling of helical trilayer graphene
• Imaging supermoiré relaxation in helical trilayer graphene
• Tunable atomically enhanced moiré Berry curvatures in twisted triple bilayer graphene
• Mean-field Modelling of Moiré Materials: A User's Guide with Selected Applications to Twisted Bilayer Graphene
• Non-Abelian Chern band in rhombohedral graphene multilayers
• Tensor network method for real-space topology in quasicrystal Chern mosaics
• Direct observation of flat bands in near-magic-angle twisted bilayer CVD graphene
• Link between thermodynamic correlation signatures and superconductivity in twisted trilayer graphene
• Higher Chern bands in helical homotrilayer transition metal dichalcogenides
• Magnetic aftereffect and Barkhausen effect in thin films of the altermagnetic candidate Mn5Si3
• Interlayer electric multipole Hall effect in twisted multilayers