On the theory of the relaxation matrix and its application to microwave transient phenomena

Enhancement of Spin-Charge Conversion in Dilute Magnetic Alloys by Kondo Screening

We derive a kinetic theory capable of dealing both with large spin-orbit coupling and Kondo screening in dilute magnetic alloys. We obtain the collision integral nonperturbatively and uncover a contribution proportional to the momentum derivative of the impurity scattering S matrix. The latter yields an important correction to the spin diffusion and spin-charge conversion coefficients, and fully captures the so-called side-jump process without resorting to the Born approximation (which fails for resonant scattering), or to otherwise heuristic derivations. We apply our kinetic theory to a quantum impurity model with strong spin-orbit, which captures the most important features of Kondo-screened Cerium impurities in alloys such as Ce_{x}La_{1-x}Cu_{6}. We find (1) a large zero-temperature spin-Hall conductivity that depends solely on the Fermi wave number and (2) a transverse spin diffusion mechanism that modifies the standard Fick's diffusion law. Our predictions can be readily verified by standard spin-transport measurements in metal alloys with Kondo impurities.

Dissipative dynamics of laser induced nonadiabatic molecular alignment

Nonadiabatic alignment induced by short, moderately intense laser pulses in molecules coupled to dissipative environments is studied within a nonperturbative density matrix theory. We focus primarily on exploring and extending a recently proposed approach [Phys. Rev. Lett. 95, 113001 (2005)], wherein nonadiabatic laser alignment is used as a coherence spectroscopy that probes the dissipative properties of the solvent. To that end we apply the method to several molecular collision systems that exhibit sufficiently varied behavior to represent a broad variety of chemical environments. These include molecules in low temperature gas jets, in room temperature gas cells, and in dense liquids. We examine also the possibility of prolonging the duration of the field free (post-pulse) alignment in dissipative media by a proper choice of the system parameters.

The Lineshape of Saturation-Broadened Transitions in the Gas Phase

The equations of motion for the density matrix are manipulated in spherical tensor form to derive formulas for the lineshapes of saturation-broadened spectroscopic transitions for gas-phase molecules. The formulas, which include consideration of the spatial degeneracy, are given for both plane-polarized and circularly polarized radiation and are in the form of weighted sums of the reciprocals of the eigenvalues of a matrix. In most practical cases, the eigenvalues will be in the form of Lorentz denominators, which expresses the lineshape as a sum of saturation-broadened Lorentz lineshapes. The approximations required to make the lineshapes equal to a sum of Karplus-Schwinger saturation-broadened lineshapes are described. The lineshape formula for plane-polarized radiation is equivalent to the continued-fraction form previously reported (R. H. Schwendeman, J. Chem. Phys. 73, 4838-4847 (1980)). Copyright 1999 Academic Press.