Chandrasekhar Hall

Magic beyond magic angle in twisted bilayer graphene

Hridis Pal

IIT Bombay

In recent years, there has been an explosion of interest in moiré materials. The simplest moiré material is twisted bilayer graphene (TBG). A TBG is formed when two layers of graphene are placed on top of each other and mutually rotated by an
arbitrary angle, leading to beautiful moiré patterns. At certain small angles of rotation (relative to AA or AB configuration) called magic angles, the electronic bands become quasiflat. With kinetic energy suppressed, electron-electron interactions dominate,
driving the system to exotic phases---some of these have already been observed experimentally, while many more have been predicted. Most of the attention, therefore, has been directed to magic angles, and the prevailing viewpoint is that away from the magic
angles, TBG is essentially similar to single layer graphene (SLG). In this talk, I will show that this viewpoint is incorrect, and demonstrate two different instances that contradict this view. First, I will show that at certain large angles of rotation far
away from magic angles, the bands can also become quasiflat. This arises due to commensuration effects and underlying topology. And second, at small angles of rotation, but away from a magic angle, the wavefunction of TBG differs from that of SLG, resulting in
observable consequences. This arises due to nonlocal terms in the interlayer coupling, typically ignored in the conventional description. These findings extend beyond TBG and are applicable to various other moire materials.