Floquet-Engineering Topological Phase Transition in Graphene Nanoribbons by Light

Quasi-one-dimensional(1D)graphene nanoribbons(GNRs)play a crucial role in advancement of nextgeneration devices.Recent studies have suggested their potential to exhibit unique symmetry-protected topological phases defined by a𝑍2 invariant.By employing both the tight-binding model and the Floquet theory,our investigation demonstrates the effective control of the topological phase within quasi-1D armchair GNRs(AGNRs)using elliptically polarized light,unveiling rich topological phase diagrams.Specifically,we observe that varying the amplitude of the light can induce transitions in the band gap(𝐸g)of AGNRs,leading to multiple changes in the system’s𝑍2 invariant.Furthermore,for heterojunctions composed of different AGNR segments,the junction state can be either created or eliminated by the application of elliptically polarized light.

Current carrying states in the disordered quantum anomalous Hall effect

In a quantum Hall effect,flat Landau levels may be broadened by disorder.However,it has been found that in the thermodynamic limit,all extended(or current carrying)states shrink to one single energy value within each Landau level.On the other hand,a quantum anomalous Hall effect consists of dispersive bands with finite widths.We numerically investigate the picture of current carrying states in this case.With size scaling,the spectrum width of these states in each bulk band still shrinks to a single energy value in the thermodynamic limit,in a power law way.The magnitude of the scaling exponent at the intermediate disorder is close to that in the quantum Hall effects.The number of current carrying states obeys similar scaling rules,so that the density of states of current carrying states is finite.Other states in the bulk band are localized and may contribute to the formation of a topological Anderson insulator.