Effective Floquet model for minimally twisted bilayer graphene

TL;DR

This paper develops an effective Floquet lattice model for minimally twisted bilayer graphene, revealing topologically distinct anomalous Floquet insulator phases and their transport properties.

Contribution

It introduces a Floquet scheme for a two-channel triangular network in twisted bilayer graphene, identifying novel topological phases without symmetry breaking.

Findings

Both one-channel and two-channel models host anomalous Floquet insulators.

The two-channel model supports a valley AFI with counterpropagating edge states.

The Floquet model's applicability is demonstrated through magnetotransport calculations.

Abstract

We construct an effective Floquet lattice model for the triangular network that emerges in interlayer-biased minimally twisted bilayer graphene and which supports two chiral channels per link for a given valley and spin. We introduce the Floquet scheme with the one-channel triangular network and subsequently extend it to the two-channel case. From the bulk topological index (winding number) and finite system calculations, we find that both cases host anomalous Floquet insulators (AFIs) with a different gap-opening mechanism. In the one-channel network, either time-reversal or in-plane inversion symmetry has to be broken to open a gap. In contrast, in the two-channel network, interchannel coupling can open a gap without breaking these symmetries yielding a valley AFI with counterpropagating edge states. This phase is topologically trivial with respect to the total winding number but robust in the absence of intervalley scattering. Finally, we demonstrate the applicability of the Floquet model with magnetotransport calculations.