Bilayer twisting as a mean to isolate connected flat bands in a Kagome lattice through Wigner crystallization

TL;DR

This paper demonstrates that bilayer twisting in Kagome lattices can isolate flat bands, leading to Wigner crystallization and potential for novel quantum phenomena, using first-principles and tight-binding models.

Contribution

It introduces a method to isolate Kagome flat bands via bilayer twisting, enabling exploration of flat-band physics and Wigner crystallization.

Findings

Bilayer twisting isolates Kagome flat bands.

Flat bands become unstable and crystallize due to interactions.

Potential for novel superconductivity and quantum Hall effects.

Abstract

The physics of flat band is novel and rich but difficult to access. In this regard, recently twisting of bilayer van der Waals (vdW)-bounded two-dimensional (2D) materials has attracted much attention, because the reduction of Brillouin zone will eventually lead to a diminishing kinetic energy. Alternatively, one may start with a 2D Kagome lattice, which already possesses flat bands at the Fermi level, but unfortunately these bands connect quadratically to other (dispersive) bands, leading to undesirable effects. Here, we propose, by first-principles calculation and tight-binding modeling, that the same bilayer twisting approach can be used to isolate the Kagome flat bands. As the starting kinetic energy is already vanishingly small, the interlayer vdW potential is always sufficiently large irrespective of the twisting angle. As such the electronic states in the (connected) flat bands become unstable against a spontaneous Wigner crystallization, which is expected to have interesting interplays with other flat-band phenomena such as novel superconductivity and anomalous quantum Hall effect.