Correlationinduced insulating topological phases at charge neutrality in twisted bilayer graphene
Abstract
Twisted bilayer graphene (TBG) provides a unique framework to elucidate the interplay between strong correlations and topological phenomena in twodimensional systems. The existence of multiple electronic degrees of freedom  charge, spin, and valley  gives rise to a plethora of possible ordered states and instabilities. Identifying which of them are realized in the regime of strong correlations is fundamental to shed light on the nature of the superconducting and correlated insulating states observed in the TBG experiments. Here, we use unbiased, signproblemfree quantum Monte Carlo simulations to solve an effective interacting lattice model for TBG at charge neutrality. Besides the usual cluster Hubbardlike repulsion, this model also contains an assisted hopping interaction that emerges due to the nontrivial topological properties of TBG. Such a nonlocal interaction fundamentally alters the phase diagram at charge neutrality, gapping the Dirac cones even for small values of the interaction. As the interaction strength increases, a sequence of different correlated insulating phases emerge, including a quantum valley Hall state with topological edge states, an intervalleycoherent insulator, and a valence bond solid. The chargeneutrality correlated insulating phases discovered here provide the soughtafter reference states needed for a comprehensive understanding of the insulating states at integer fillings and the proximate superconducting states of TBG.
 Publication:

arXiv eprints
 Pub Date:
 April 2020
 arXiv:
 arXiv:2004.12536
 Bibcode:
 2020arXiv200412536D
 Keywords:

 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 8+6 pages, 3+4 figures, 0+2 table