First principles quasiparticle damping rates in bulk lead

First principles calculations of the damping rates (inverse inelastic lifetimes) of low energy quasiparticles in bulk Pb are presented. Damping rates are obtained both for excited electrons and holes with energies up to 8 eV on a set of k vectors throughout the Brillouin zone (BZ). Strong localization effects in the calculated lifetimes are found. Averaged over the BZ inelastic lifetimes versus quasiparticle energy are reported as well. In addition, the effect of the spin-orbit induced splitting in the band structure on the calculated lifetimes in Pb is investigated.Comment: 10 pages, 8 figures, 5 table

Pressure on charged domain walls and additional imprint mechanism in ferroelectrics

The impact of free charges on the local pressure on a charged ferroelectric domain wall produced by an electric field has been analyzed. A general formula for the local pressure on a charged domain wall is derived considering full or partial compensation of bound polarization charges by free charges. It is shown that the compensation can lead to a very strong reduction of the pressure imposed on the wall from the electric field. In some cases this pressure can be governed by small nonlinear effects. It is concluded that the free charge compensation of bound polarization charges can lead to substantial reduction of the domain wall mobility even in the case when the mobility of free charge carriers is high. This mobility reduction gives rise to an additional imprint mechanism which may play essential role in switching properties of ferroelectric materials. The effect of the pressure reduction on the compensated charged domain walls is illustrated for the case of 180-degree ferroelectric domain walls and of 90-degree ferroelectric domain walls with the head-to-head configuration of the spontaneous polarization vectors.Comment: subm. to PRB. This verion is extended by appendi

Random Operator Approach for Word Enumeration in Braid Groups

We investigate analytically the problem of enumeration of nonequivalent primitive words in the braid group B_n for n >> 1 by analysing the random word statistics and the target space on the basis of the locally free group approximation. We develop a "symbolic dynamics" method for exact word enumeration in locally free groups and bring arguments in support of the conjecture that the number of very long primitive words in the braid group is not sensitive to the precise local commutation relations. We consider the connection of these problems with the conventional random operator theory, localization phenomena and statistics of systems with quenched disorder. Also we discuss the relation of the particular problems of random operator theory to the theory of modular functionsComment: 36 pages, LaTeX, 4 separated Postscript figures, submitted to Nucl. Phys. B [PM

Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems

We report a theoretical study of the quasiparticle lifetime and the quasiparticle mean free path caused by inelastic electron-electron scattering in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based on spin-polarized calculations, which are performed within the $GW$ approximation for equiatomic and Co- and Ni-rich compounds, as well as for their constituents. We mainly focus on the spin asymmetry of the quasiparticle properties, which leads to the spin-filtering effect experimentally observed in spin-dependent transport of hot electrons and holes in the systems under study. By comparing with available experimental data on the attenuation length, we estimate the contribution of the inelastic mean free path to the latter.Comment: 10 pages, 10 figure

Longest increasing subsequence as expectation of a simple nonlinear stochastic PDE with a low noise intensity

We report some new observation concerning the statistics of Longest Increasing Subsequences (LIS). We show that the expectation of LIS, its variance, and apparently the full distribution function appears in statistical analysis of some simple nonlinear stochastic partial differential equation (SPDE) in the limit of very low noise intensity.Comment: 6 pages, 4 figures, reference adde

Variational solution of the T-matrix integral equation

We present a variational solution of the T-matrix integral equation within a local approximation. This solution provides a simple form for the T matrix similar to Hubbard models but with the local interaction depending on momentum and frequency. By examining the ladder diagrams for irreducible polarizability, a connection between this interaction and the local-field factor is established. Based on the obtained solution, a form for the T-matrix contribution to the electron self-energy in addition to the GW term is proposed. In the case of the electron-hole multiple scattering, this form allows one to avoid double counting.Comment: 7 pages, 7 figure

Topological relaxation of entangled flux lattices: Single vs collective line dynamics

A symbolic language allowing to solve statistical problems for the systems with nonabelian braid-like topology in 2+1 dimensions is developed. The approach is based on the similarity between growing braid and "heap of colored pieces". As an application, the problem of a vortex glass transition in high-T_c superconductors is re-examined on microscopic levelComment: 4 pages (revtex), 4 figure