One-pion exchange current corrections for nuclear magnetic moments in relativistic mean field theory

The one-pion exchange current corrections to isoscalar and isovector magnetic moments of double-closed shell nuclei plus and minus one nucleon with $A=15,17,39$ and 41 have been studied in the relativistic mean field (RMF) theory and compared with previous relativistic and non-relativistic results. It has been found that the one-pion exchange current gives a negligible contribution to the isoscalar magnetic moments but a significant correction to the isovector ones. However, the one-pion exchange current doesn't improve the description of nuclear isovector magnetic moments for the concerned nuclei.Comment: 9 pages, 1 figure, 3 table

Properties of a two orbital model for oxypnictide superconductors: Magnetic order, B_2g spin-singlet pairing channel, and its nodal structure

A two orbital model for the new Fe-based superconductors is studied using the Lanczos method as well as pairing mean-field approximations. Our main goals are (i) to provide a comprehensive analysis of this model using numerical techniques with focus on half-filling and on the state with two more electrons than half-filling and (ii) to investigate the nodal structure of the mean-field superconducting state and compare the results with angle-resolved photoemission data. In particular, we provide evidence that at half-filling spin 'stripes', as observed experimentally, dominate over competing states. Depending on parameters, the state with two more electrons added to half filling is either triplet or singlet. Since experiments suggest spin singlet pairs, our focus is on this state. Under rotation, it transforms as the B_2g representation of the D_4h group. We also show that the s+/- pairing operator transforms as A_1g and becomes dominant only in an unphysical regime of the model where the undoped state is an insulator. For robust values of the effective electronic attraction producing the Cooper pairs, assumption compatible with recent angle-resolved photoemission (ARPES) results that suggesting small Cooper-pair size, the nodes of the two-orbital model are found to be located only at the electron pockets. Since recent ARPES efforts have searched for nodes at the hole pockets or only in a few directions at the electron pockets, our results for the nodal distribution may help to guide future experiments. More in general, the investigations reported here aim to establish several of the properties of the two orbital model. Only a detailed comparison with experiments will clarify how far this simple model present a valid description of the Fe pnictides

A molecular-dynamics algorithm for mixed hard-core/continuous potentials

We present a new molecular-dynamics algorithm for integrating the equations of motion for a system of particles interacting with mixed continuous/impulsive forces. This method, which we call Impulsive Verlet, is constructed using operator splitting techniques similar to those that have been used successfully to generate a variety molecular-dynamics integrators. In numerical experiments, the Impulsive Verlet method is shown to be superior to previous methods with respect to stability and energy conservation in long simulations.Comment: 18 pages, 6 postscript figures, uses rotate.st

Nonlinear Aggregation-Diffusion Equations: Radial Symmetry and Long Time Asymptotics

We analyze under which conditions equilibration between two competing effects, repulsion modeled by nonlinear diffusion and attraction modeled by nonlocal interaction, occurs. This balance leads to continuous compactly supported radially decreasing equilibrium configurations for all masses. All stationary states with suitable regularity are shown to be radially symmetric by means of continuous Steiner symmetrization techniques. Calculus of variations tools allow us to show the existence of global minimizers among these equilibria. Finally, in the particular case of Newtonian interaction in two dimensions they lead to uniqueness of equilibria for any given mass up to translation and to the convergence of solutions of the associated nonlinear aggregation-diffusion equations towards this unique equilibrium profile up to translations as $t\to\infty$

Configuration mixing of angular-momentum projected triaxial relativistic mean-field wave functions

The framework of relativistic energy density functionals is extended to include correlations related to the restoration of broken symmetries and to fluctuations of collective variables. The generator coordinate method is used to perform configuration mixing of angular-momentum projected wave functions, generated by constrained self-consistent relativistic mean-field calculations for triaxial shapes. The effects of triaxial deformation and of $K$-mixing is illustrated in a study of spectroscopic properties of low-spin states in $^{24}$Mg.Comment: 15 pages, 11 figures, 4 tables, accepted for publication in Phys. Rev.

Intermediate-statistics quantum bracket, coherent state, oscillator, and representation of angular momentum (su(2)) algebra

In this paper, we first discuss the general properties of an intermediate-statistics quantum bracket, $[ u,v]_{n}=uv-e^{i2\pi /(n+1)}vu$, which corresponds to intermediate statistics in which the maximum occupation number of one quantum state is an arbitrary integer, $n$. A further study of the operator realization of intermediate statistics is given. We construct the intermediate-statistics coherent state. An intermediate-statistics oscillator is constructed, which returns to bosonic and fermionic oscillators respectively when $n\to \infty$ and $n=1$. The energy spectrum of such an intermediate-statistics oscillator is calculated. Finally, we discuss the intermediate-statistics representation of angular momentum ($su(2)$) algebra. Moreover, a further study of the operator realization of intermediate statistics is given in the Appendix.Comment: 12 pages, no figures. Revte

Optical Control of Topological Quantum Transport in Semiconductors

Intense coherent laser radiation red-detuned from absorption edge can reactively activate sizable Hall type charge and spin transport in n-doped paramagnetic semiconductors as a consequence of k-space Berry curvature transferred from valence band to photon-dressed conduction band. In the presence of disorder, the optically induced Hall conductance can change sign with laser intensity.Comment: to appear in Phys. Rev. Let

Lifshitz-Slyozov Scaling For Late-Stage Coarsening With An Order-Parameter-Dependent Mobility

The coarsening dynamics of the Cahn-Hilliard equation with order-parameter dependent mobility, $\lambda(\phi) \propto (1-\phi^2)^\alpha$, is addressed at zero temperature in the Lifshitz-Slyozov limit where the minority phase occupies a vanishingly small volume fraction. Despite the absence of bulk diffusion for $\alpha>0$, the mean domain size is found to grow as $\propto t^{1/(3+\alpha)}$, due to subdiffusive transport of the order parameter through the majority phase. The domain-size distribution is determined explicitly for the physically relevant case $\alpha = 1$.Comment: 4 pages, Revtex, no figure