We study the effect of electron spill-out and of nonlocality on the propagation of light inside a gap between two semi-infinite metallic regions. We compare the predictions of a local response model ...taking into account only the spill-out, to the predictions of a quantum hydrodynamic model able to take both phenomena into account. We show that only the latter is able to correctly retrieve the correct limit when the gap closes, while the local model suffers from undesirable features (divergence of the fields, overestimation of the losses). Finally, we show that, to a certain extent, the correct results can be retrieved using a simple local approach without spill-out or conventional Thomas-Fermi approximation, but considering an effective gap width.
The single graphene layer is a novel material consisting of a flat monolayer of carbon atoms packed in a two-dimensional honeycomb-lattice, in which the electron dynamics is governed by the Dirac ...equation. A pseudo-spin phase-space approach based on the Wigner-Weyl formalism is used to describe the transport of electrons in graphene including quantum effects. Our full-quantum mechanical representation of the particles reveals itself to be particularly close to the classical description of the particle motion. We analyze the Klein tunneling and the correction to the total current in graphene induced by this phenomenon. The equations of motion are analytically investigated and some numerical tests are presented. The temporal evolution of the electron-hole pairs in the presence of an external electric field and a rigid potential step is investigated. The connection of our formalism with the Barry-phase approach is also discussed.
The Wigner-function approach is used to describe an interband transition of electrons between the conduction and the valence band in a semiconductor under the action of an electric field in the ...uniform field approximation. The quantum dynamics is governed by the k·p Hamiltonian; an approximate closed-form solution is obtained by an iterative procedure that exploits the different time scales on which the intraband and interband dynamical variables evolve. The results of this approximation are compared with a numerical solution, showing an excellent agreement, which paves the way for its use in more realistic situations where the numerical solution is much harder to obtain.
We study of the ultrafast dynamics of the atomic angular momentum in ferrimagnets irradiated by laser pulses. My apply a quantum atomistic spin approach based on the Monte Carlo technique. Our model ...describes the coherent transfer of angular momentum between the spin and the orbital momentum as well as the quenching of the orbital momentum induced by the lattice field. The Elliott-Yafet collision mechanism is also included. We focus on elementary mechanisms that lead to the dissipation of the total angular momentum in a rare earth-transition metal (RE-TM) alloy in which the two sublattices have opposite spin orientation. Our model shows that the observed ultrafast quenching of the magnetization can be explained microscopically by the transfer of spin between the sublattices and by the quenching of the localized orbital angular momentum.
The production of a Bose-Einstein condensate made of positronium may be feasible in the near future. Below the condensation temperature, the positronium collision process is modified by the presence ...of the condensate. This makes the theoretical description of the positronium kinetics at low temperature challenging. Based on the quasi-particle Bogoliubov theory, we describe the many-body particle-particle collision in a simple manner. We find that, in a good approximation, the full positronium-positronium interaction can be described by an effective scattering length. Our results are general and apply to different species of bosons. The correction to the bare scattering length is expressed in terms of a single dimensionless parameter that completely characterizes the condensate.
We present a mathematical study of a two-band quantum kinetic transport model. The multiband model, derived in the envelope function theory, is designed to describe the dynamics in semiconductor ...devices when the interband conduction-valence transition cannot be neglected. The Wigner formulation consists of a four-by-four system, containing two effective mass Wigner equations (one for the electron in conduction band and one for the valence band) coupled by pseudo-differential operators arising from the electric field in the semiconductor. The existence and uniqueness of a solution to the initial value problem are proved in a L
2
-setting for sufficiently regular electric potentials. An extension of the single band splitting-scheme algorithm is presented to solve the one-dimensional system for a bounded domain. Finally, we show some numerical results concerning the simulation of an interband resonant diode.
Graphene is a novel material constituted by a two-dimensional carbon lattice. The electron dynamics in graphene is governed by the Dirac equation. The Wigner-Weyl formalism is used to describe the ...transport of electrons in graphene including quantum effects. A diagonalization procedure regarding the pseudo-spin degree of freedom is proposed. Our approach highlights the effect of Klein tunneling and we study the correction of the total current in intrinsic graphene induced by this phenomena. The connection of our formalism with the Berry phase approach is also investigated.
We present a dynamical model that successfully explains the observed time evolution of the magnetization in diluted magnetic semiconductor quantum wells after weak laser excitation. Based on the ...pseudo-fermion formalism and a second order many-particle expansion of the exact p-d exchange interaction, our approach goes beyond the usual mean-field approximation. It includes both the sub-picosecond demagnetization dynamics and the slower relaxation processes which restore the initial ferromagnetic order in a nanosecond time scale. In agreement with experimental results, our numerical simulations show that, depending on the value of the initial lattice temperature, a subsequent enhancement of the total magnetization may be observed within a time scale of few hundreds of picoseconds.
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