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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:32 |
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Conference: Bucharest University Faculty of Physics 2001 Meeting
Section: Theoretical Physics and Applied Mathematics
Title:
THE FLOQUET SOLUTION FOR QUASI-FREE ELECTRONS IN TWO-DIMENSIONAL CRYSTAL LATTICE
Authors:
Radu-Paul Lungu
Affiliation:
Department of Physics, University of Bucharest, Bucharest-Magurele, R-76900 Romania
E-mail
Keywords:
Abstract:
The quasi-energies and the reduced Floquet vectors corresponding to an electron in 2-dimensions, interacting with a time-dependent monochromatic, linearly polarized electromagnetic field, and in the presence of a weak, spatial periodic (in both directions) are calculated. This computations are performed using a variant of the stationary perturbation theory in the extended Hilbert space adapted for the eigenvalue equation of the Floquet Hamiltonian.
The perturbative corrections, in the second order, (for the quasi-energies and for the Floquet reduced vectors) show the following remarcable particularities:
a) the Floquet eigen-functions have an Bloch form, but with an effective wave vector; this ``effective wave vector` has a component on the direction of the radiation field that is time-periodic, and the other component is static;
b) the quasi-energy spectrum has gaps at the boundaries of the Brillouin zones, and on the direction of the radiation field the gaps are dependent on the electric field intensity; moreover, for some values of the electric field intensity (or for the radiation frequency) it is posible to vanish these gaps.
These results can be considered as the Floquet variant of the quasi-free electron model from the conservative theory.
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