Spectroscopy of Twisted Bilayer Graphene Correlated Insulators

Abstract

We calculate STM signatures of correlated ground-states at integer filling of the magic angle twisted bilayer graphene narrow bands. First, we compute the fully-interacting TBG spectral function at ±4 electrons/moiré unit cell and show that it can be used to experimentally validate the strong-coupling approach. Although variation exists in the data, we find experimental evidence for the strong-coupling regime. For all other integer fillings of the flat bands, we consider the spatial features of the corresponding spectral functions of many states in the large degenerate ground-state manifold, and assess the possibility of Kekulé distortion (KD) emerging at the graphene lattice scale. Remarkably, we find that coupling the two opposite graphene valleys in the intervalleycoherent (IVC) TBG insulators does not always result in KD. As an example, we show that the K-IVC state and its nonchiral U (4) rotations do not exhibit any KD, while T-IVC does. We analyze 14 different many-body correlated states and show that their combined STM/Chern number signal can be used to uniquely determine the nature of the many-body ground-state. Their STM signal and features are obtained over a large range of energies and model parameters.

Skyrmions in twisted bilayer graphene: stability, pairing, and crystallization

“…Measuring pseudospin textures at even integer filling is trickier since experimental techniques are not able to directly couple to the valley degree of freedom. IVC generally leads to √ 3 × √ 3 spatial order at the microscopic graphene scale, but the T -symmetry of the KIVC insulator means that it does not exhibit a Kekulé density distortion (KD) 101,102 . Paired skyrmions preserve T and hence do not give rise to KD 102 .…”

Anderson's theorem for correlated insulating states in twisted bilayer graphene

“…A prime candidate for understanding the correlated insulating phases, which occur near even integer fillings of the moiré flat bands are Kramers intervalley coherent (K-IVC) states [18][19][20][21][22][23][24]. These states exhibit a pattern of magnetization currents, which triple the graphene unit cell, thereby breaking the lattice translation symmetry as well as time reversal.…”