Multi-flat bands and strong correlations in Twisted Bilayer Boron Nitride

Abstract: In a groundbreaking experimental advance it was recently shown that by stacking two sheets of graphene atop of each other at a twist angle close to one of the so called "magic angles", an effective two-dimensional correlated system emerges. In this system the kinetic energy of the low-energy electrons is much reduced and consequently interactions become very relevant, providing a new platform into the physics of two-dimensional correlated materials. Evidence of a proposed Mott insulating as well as superconducting state in these highly tunable systems has spurred much attention as they could pave the way to understanding long-standing questions of high-$T_c$ superconductivity or provide candidate systems for topological chiral superconductors; key to highly relevant quantum technologies. Here, we demonstrate that twisted bilayer boron nitride (TBBN) is an exciting and even richer alternative to twisted bilayer graphene (TBG). Crucially, we show that in TBBN multiple flat bands emerge without having to fine tuning close to a "magic angle" that upon doping lead to correlated phases of matter (insulating and superconducting). TBBN could thus be much less sensitive to small deviations in the twist angle and therefore provide a particularly suited experimental platform to study correlation physics in two dimensions. Furthermore, we find that in marked contrast to TBG at small twist angle families of 2,4 and 6-fold degenerate, well separated, bands emerge within the gap, considerably broadening the addressable physics.