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(a) Schematic plot of the graphene-like Kane-Mele model subjected to circularly polarized radiation. (b) Schematic plot of our model device. The central region is a zigzag nanoribbon with NL chains and NK atom sites per chain. It is connected to two semi-infinite graphene nanoribbons of the same width. (c) Classical picture on the motion (blue) in x-y plane of an electron (green dot) which is driven by the electric field E (red) of a circularly polarized field. The frequency of the driving field is Ω, and the phase lag between the rotations of the electric field E and the electron displacement r is φ 0.
Time-averaged conductance G as a function of the Fermi energy EF and the parameter of ac field intensity A op. The other parameters are given in the text. At equilibrium, the system is in insulating states and the conductance is suppressed. As we increase A op, one can clearly see step structures in the conductance with the step height e 2/h. Such step structure is destroyed at very large A op.
Evolution of the time-averaged conductance G with increasing ac field intensity A op for fixed Fermi energy EF = 0.04 t 0. The other parameters are identical with those in Fig. 2. The arrows, which are labeled as (a)-(c) for later reference, mark typical cases where the conductance is close to the integer multiple of e 2/h.
(a)-(c) Quasi-energy spectra for the respective cases labeled as (a)-(c) in Fig. 3. L is the distance of two nearest zigzag chains in the ribbon (d). Close to a given energy E = 0.075 t 0 (the dashed line), there are four states labeled as (a)-(d) in (c). (d) The norm of the wavefunctions , where i is the atom index in one zigzag chain, for the energy states labeled in (c).
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