Broken-symmetry states at half-integer band fillings in twisted bilayer graphene

Non-coplanar magnetism, topological density wave order and emergent symmetry at half-integer filling of moiré Chern bands

“…Moreover, signatures of symmetry broken Chern insulators (SBCIs) with |C| " 1 at conduction band filling ν " 7{2 in both TDBG [18] and TMBG [19] highlight the intertwining of topology and translational symmetry breaking order at non-integer filling fractions in these moiré systems. Correlated states at half-integer band fillings are also seen in experiments on related graphene based moiré materials [20][21][22].…”

Phase transition from a nonmagnetic to a ferromagnetic state in a twisted bilayer graphene nanoflake: the role of electronic pressure on the magic-twist

“…The success in fine-tuning the rotational alignment between the layer in these structures during the synthesis to tune the IEC has made it possible to observe these exotic phases. For example, twisted bilayer graphene (BLG), a widely studied material, 1–48 has been reported to exhibit a variety of intriguing correlated states ranging from superconductivity 2–5,17,24,31,35,37,46 to ferromagnetism 13–15,30 at a small magic twist angle of ∼1°. The emergence of dispersionless energy minibands 7,8,18–23,26–29,33,34,47 in the vicinity of the Fermi energy at ∼1° in twisted BLG leads to complete suppression of the quasiparticle's kinetic energy in frontier states and enhancement of electron–electron interaction strength at the magic angle, which gives rise to these observed, strong IEC-driven correlated phases.…”

Band structure sensitive photoresponse in twisted bilayer graphene proximitized with WSe2

“…8,9 More recently, it has been shown that tBLG proximitized with a layer of WSe 2 can not only lead to orbital ferromagnetism 10 but also the broken symmetry states at half-integer fillings. 11 Although different transport measurements have shed light on the rich-phase diagram of WSe 2 /tBLG devices, the understanding of light-matter interaction in such systems remains elusive as previous experiments in this direction are limited only to twisted graphene layers [12][13][14] or twisted layers of transition metal dichalcogenides. 15 It has been demonstrated and well established that photoresponse in single-layer graphene enhances by orders of magnitude when proximitized with TMDC, owing to the efficient charge separation at the heterostructure interface and the photogating effect.…”

“…The intrinsic electron-hole asymmetry in WSe 2 proximitized tBLG band structure is well established. 10,11,38 Theoretical calculations on BLG/WSe 2 heterostructures show that the low-energy valence bands in BLG originate from the non-dimer carbon atom orbitals in the graphene layer adjacent to WSe 2 , while the conduction band is formed by non-dimer orbitals in other layer. 39 It leads to a larger overlap between wave functions of WSe 2 and the graphene orbitals in the valence band as compared to the conduction band, which can affect the charge transfer efficiency.…”

“…The desired vertical heterostructure is assembled using a dry transfer technique involving the tear and stack method reported in ref. 11 and 23. The stack is etched to Hall bar geometry, and Ohmic edge contacts are defined by e-beam lithography followed by Cr/Au (5/50 nm) thermal evaporation.…”