Abstract
Based on a solution of the Floquet Hamiltonian we have studied the time evolution of electronic states in graphene nanoribbons driven out of equilibrium by time-dependent electromagnetic fields in different regimes of intensity, polarization, and frequency. We show that the time-dependent band structure contains many unconventional features that are not captured by considering the Floquet eigenvalues alone. By analyzing the evolution in time of the state population we have identified regimes for the emergence of time-dependent edge states responsible for charge oscillations across the ribbon.
Highlights
When the field is applied for a sufficiently long time electrons reach a nonequilibrium steady state characterized by a periodic time-dependence of the wave functions and, of the expectation values of any observable [12, 13]
In this paper we focus on this time-dependence, looking for the time evolution of some relevant quantities such as energy and charge density
We will consider the prototypical case of graphene that under the influence of circularly polarized light exhibits in its Floquet band structure the distinctive characteristics of a 2D Chern insulator, namely, a gap in 2D and linear dispersive edge states in 1D [9, 11, 14, 15]
Summary
When the field is applied for a sufficiently long time (pulse duration much larger than the field oscillation period) electrons reach a nonequilibrium steady state characterized by a periodic time-dependence of the wave functions and, of the expectation values of any observable [12, 13]. We may conclude this analysis of Floquet quasi-energies by noticing that only circularly polarized fields of sufficient strength may induce Floquet edge states with a significant linear dispersion.
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