Topological flat bands in time-periodically driven uniaxial strained graphene nanoribbons

TL;DR

This paper investigates how time-periodic driving and uniaxial strain in graphene nanoribbons lead to the emergence of topologically non-trivial flat bands at specific quasienergies, revealing new topological phases and potential experimental realizations.

Contribution

It demonstrates the emergence of topological flat bands at zero and π quasienergies in driven strained graphene, and constructs the topological phase diagram for this system.

Findings

Flat bands appear at zero and π quasienergies.

Topological flat bands connect band touching points with opposite Berry phases.

A topological phase diagram for the driven strained graphene system is developed.

Abstract

We study the emergence of electronic non-trivial topological flat bands in time-periodically driven strained graphene within a tight binding approach based on the Floquet formalism. In particular, we focus on uniaxial spatially periodic strain since it can be mapped onto an effective one-dimensional system. Also, two kinds of time-periodic driving are considered: a short pulse (delta kicking) and a sinusoidal variation (harmonic driving). We prove that for special strain wavelengths, the system is described by a two level Dirac Hamiltonian. Even though the study case is gapless, we find that topologically non-trivial flat bands emerge not only at zero-quasienergy but also at $\pm\pi$ quasienergy, the latter being a direct consequence of the periodicity of the Floquet space. Both kind of flat bands are thus understood as dispersionless bands joining two inequivalent touching band points with opposite Berry phase. This is confirmed by explicit evaluation of the Berry phase in the touching band points' neighborhood. Using that information, the topological phase diagram of the system is built. Additionally, the experimental feasibility of the model is discussed and two methods for the experimental realization of our model are proposed.