82,436 research outputs found

### Size dependence of second-order hyperpolarizability of finite periodic chain under Su-Schrieffer-Heeger model

The second hyperpolarizability $\gamma_N(-3\omega\omega,\omega,\omega)$ of
$N$ double-bond finite chain of trans-polyactylene is analyzed using the
Su-Schrieffer-Heeger model to explain qualitative features of the
size-dependence behavior of $\gamma_N$. Our study shows that $\gamma_N/N$ is
{\it nonmonotonic} with $N$ and that the nonmonotonicity is caused by the
dominant contribution of the intraband transition to $\gamma_N$ in polyenes.
Several important physical effects are discussed to reduce quantitative
discrepancies between experimental and our resultsComment: 3 figures, 1 tabl

### Uniqueness of Bessel models: the archimedean case

In the archimedean case, we prove uniqueness of Bessel models for general
linear groups, unitary groups and orthogonal groups.Comment: 22 page

### Some symmetry properties of spin currents and spin polarizations in multi-terminal mesoscopic spin-orbit coupled systems

We study theoretically some symmetry properties of spin currents and spin
polarizations in multi-terminal mesoscopic spin-orbit coupled systems. Based on
a scattering wave function approach, we show rigorously that in the equilibrium
state no finite spin polarizations can exist in a multi-terminal mesoscopic
spin-orbit coupled system (both in the leads and in the spin-orbit coupled
region) and also no finite equilibrium terminal spin currents can exist. By use
of a typical two-terminal mesoscopic spin-orbit coupled system as the example,
we show explicitly that the nonequilibrium terminal spin currents in a
multi-terminal mesoscopic spin-orbit coupled system are non-conservative in
general. This non-conservation of terminal spin currents is not caused by the
use of an improper definition of spin current but is intrinsic to
spin-dependent transports in mesoscopic spin-orbit coupled systems. We also
show that the nonequilibrium lateral edge spin accumulation induced by a
longitudinal charge current in a thin strip of \textit{finite} length of a
two-dimensional electronic system with intrinsic spin-orbit coupling may be
non-antisymmetric in general, which implies that some cautions may need to be
taken when attributing the occurrence of nonequilibrium lateral edge spin
accumulation induced by a longitudinal charge current in such a system to an
intrinsic spin Hall effect.Comment: 11 pages, 6 figure

### Time Dependent Theory for Random Lasers

A model to simulate the phenomenon of random lasing is presented. It couples
Maxwell's equations with the rate equations of electronic population in a
disordered system. Finite difference time domain methods are used to obtain the
field pattern and the spectra of localized lasing modes inside the system. A
critical pumping rate $P_{r}^{c}$ exists for the appearance of the lasing
peaks. The number of lasing modes increase with the pumping rate and the length
of the system. There is a lasing mode repulsion. This property leads to a
saturation of the number of modes for a given size system and a relation
between the localization length $\xi$ and average mode length $L_m$.Comment: 8 pages. Send to PR

### Non-equilibrium spin polarization effects in spin-orbit coupling system and contacting metallic leads

We study theoretically the current-induced spin polarization effect in a
two-terminal mesoscopic structure which is composed of a semiconductor
two-dimensional electron gas (2DEG) bar with Rashba spin-orbit (SO) interaction
and two attached ideal leads. The nonequilibrium spin density is calculated by
solving the scattering wave functions explicitly within the ballistic transport
regime. We found that for a Rashba SO system the electrical current can induce
spin polarization in the SO system as well as in the ideal leads. The induced
polarization in the 2DEG shows some qualitative features of the intrinsic spin
Hall effect. On the other hand, the nonequilibrium spin density in the ideal
leads, after being averaged in the transversal direction, is independent of the
distance measured from the lead/SO system interface, except in the vicinity of
the interface. Such a lead polarization effect can even be enhanced by the
presence of weak impurity scattering in the SO system and may be detectable in
real experiments.Comment: 6 pages,5 figure

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