We study the spin dynamics of carriers due to the Rashba interaction in semiconductor quantum disks and wells after excitation with light with orbital angular momentum. We find that although twisted light transfers orbital angular momentum to the exc
ited carriers and the Rashba interaction conserves their total angular momentum, the resulting electronic spin dynamics is essentially the same for excitation with light with orbital angular momentum $l=+|l|$ and $l=-|l|$. The differences between cases with different values of $|l|$ are due to the excitation of states with slightly different energies and not to the different angular momenta per se, and vanish for samples with large radii where a $k$-space quasi-continuum limit can be established. These findings apply not only to the Rashba interaction but also to all other envelope-function approximation spin-orbit Hamiltonians like the Dresselhaus coupling.
In this article we explore how structural parameters of composites filled with one-dimensional, electrically conducting elements (such as sticks, needles, chains, or rods) affect the percolation properties of the system. To this end, we perform Monte
Carlo simulations of asymmetric two-dimensional stick systems with anisotropic alignments. We compute the percolation probability functions in the direction of preferential orientation of the percolating objects and in the orthogonal direction, as functions of the experimental structural parameters. Among these, we considered the average length of the sticks, the standard deviation of the length distribution, and the standard deviation of the angular distribution. We developed a computer algorithm capable of reproducing and verifying known theoretical results for isotropic networks and which allows us to go beyond and study anisotropic systems of experimental interest. Our research shows that the total electrical anisotropy, considered as a direct consequence of the percolation anisotropy, depends mainly on the standard deviation of the angular distribution and on the average length of the sticks. A conclusion of practical interest is that we find that there is a wide and well-defined range of values for the mentioned parameters for which it is possible to obtain reliable anisotropic percolation under relatively accessible experimental conditions when considering composites formed by dispersions of sticks, oriented in elastomeric matrices.
We examine theoretically the intersubband transitions induced by laser beams of light with orbital angular momentum (twisted light) in semiconductor quantum wells at normal incidence. These transitions become possible in the absence of gratings thank
s to the fact that collimated laser beams present a component of the lights electric field in the propagation direction. We derive the matrix elements of the light-matter interaction for a Bessel-type twisted-light beam represented by its vector potential in the paraxial approximation. Then, we consider the dynamics of photo-excited electrons making intersubband transitions between the first and second subbands of a standard semiconductor quantum well. Finally, we analyze the light-matter matrix elements in order to evaluate which transitions are more favorable for given orbital angular momentum of the light beam in the case of small semiconductor structures.
