Recently research into graphene nanoribbon(GNR) has been extensively conducted and it is known to be applicable to wide range of areas such as optical fibre, semiconductor, transistor and filter, etc.
We have already proved that the honeycomb nanoribbon could cause the interesting topological phase transition from a trivial phase to a topological phase as we change the strength of the circularly polarized laser light.
Gap-closing and the appearance of the two crossing edge states in the quasi energy spectrum are also accompanied by the phase transition.
The results support the idea that not only the static system, but also the time periodically driven system could be topologically robust even in nonequilibrium situation. Bulk properties are also important and have to be considered in relation to the edge states.
We have studied the change of the first Chern number as the laser light intensity grows for the different values of frequencies of the light. As we decrease the frequency from high value to approximately 6.0, the system becomes topological due to the sudden change in the value of the first Chern number from 0 to-1 and the emergence of the crossing edge states in the quasi energy spectrum.
However, the nontrivial behavior which is beyond our expectation is observed when the value of the frequency of the irradiating laser field reaches a certain critical value. The first Chern number can take several values when we increase the laser intensity from 0 to 1. It is particularly remarkable that the topological phase induced by the light with a moderate intensity (at most, 0.5) in this frequency range does not have the crossing edge states that are the typical characters, but has nonzero value of the first Chern number.
Our results will be useful for either experimenters or theorists whose aims are to engineer the topological properties of the materials for their various purposes.
The result has been published in "International Journal of Modern Physics B" under the title of "Bulk-edge correspondence for Floquet topological phases in honeycomb nanoribbon" (https://doi.org/10.1142/S0217979223501540).
