Topological gaps by twisting

Twisted bilayered systems such as bilayered graphene exhibit remarkable properties such as superconductivity at magic angles and topological insulating phases. For generic twist angles, the bilayers are truly quasiperiodic, a fact that is often overlooked and that has consequences which are largely unexplored. Herein, we uncover that twisted n-layers host intrinsic higher dimensional topological phases, and that those characterized by second Chern numbers can be found in twisted bi-layers. We employ phononic lattices with interactions modulated by a second twisted lattice and reveal Hofstadter-like spectral butterflies in terms of the twist angle, which acts as a pseudo magnetic field. The phason provided by the sliding of the layers lives on 2n-tori and can be used to access and manipulate the edge states. Our work demonstrates how multi-layered systems are virtual laboratories for studying the physics of higher dimensional quantum Hall effect, and can be employed to engineer topological pumps via simple twisting and sliding. All aperiodic systems display an intrinsic degree of freedom, called the phason, and here it is shown that the phason space for twisted bilayered systems is a 2-torus. As a consequence, these systems host the physics of 4-dimensional integer quantum Hall effect, which can be accessed by simply sliding the layers relative to each other.

Automated summary

Twisted bilayered systems exhibit higher dimensional topological phases and 4D integer quantum Hall effect, which can be accessed by sliding the layers relative to each other.