Structure of the σ\sigma-meson and diamagnetism of the nucleon

The structure of the $\sigma$ meson and the diamagnetism of the nucleon are shown to be topics which are closely related to each other. Arguments are found that the $\sigma$ meson couples to two photons via its non-strange $q\bar{q}$ structure component. This ansatz leads to a quantitative explanation of the $t$-channel component of the difference of electromagnetic polarizabilities, (\alpha-\beta)^t$, containing the diamagnetism of the nucleon. The prediction is$(\alpha-\beta)^t_{p,n}=(5\alpha_e g_{\pi MM})/(6\pi^2 m^2_\sigma f_\pi)=15.3$in units of$10^{-4}{\rm fm}^3$to be compared with the experimental value$(\alpha-\beta)^t_p=15.1\pm 1.3$for the proton and$(\alpha-\beta)^t_n=14.8\pm 2.7$for the neutron. The equivalent approach to exploit the$\pi\pi$structure component of the$\sigma$meson via the BEFT sum rule leads to$(\alpha-\beta)^t_{p,n}=14\pm 2$, what also is in agreement with the experimental results.Comment: Contribution made by Martin Schumacher to the International Workshop on the Physics of Excited Baryons, 12 - 15 Oct. 2005, Tallahasse, Florida US

Edge spin accumulation: spin Hall effect without bulk spin current

Spin accumulation in a 2D electron gas with Rashba spin-orbit interaction subject to an electric field can take place without bulk spin currents (edge spin Hall effect). This is demonstrated for the collisional regime using the non-equilibrium distribution function determined from the standard Boltzmann equation. Spin accumulation originates from interference of incident and reflected electron waves at the sample boundary.Comment: 4 pages, 3 figure

Triplet contribution to the Josephson current in the nonequilibrium superconductor/ferromagnet/superconductor junction

The Josephson current through a long s-wave superconductor/weak ferromagnet/s-wave superconductor weak link is studied theoretically in the regime of nonequilibrium spin-dependent occupation of electron states in the ferromagnetic intelayer. While under the considered nonequilibrium condition the standard supercurrent, carried by the singlet part of current-carrying density of states, is not modified, the additional supercurrent flowing via the triplet part of the current-carrying density of states appears. Depending on voltage, controlling the particular form of spin-dependent nonequilibrium in the interlayer, this additional current can enhance or reduce the usual current of the singlet component and also switch the junction between 0- and $\pi$-states.Comment: 4 pages, 1 figur

Magnetoresistance due to edge spin accumulation

Because of spin-orbit interaction, an electrical current is accompanied by a spin current resulting in spin accumulation near the sample edges. Due again to spin-orbit interaction this causes a small decrease of the sample resistance. An applied magnetic field will destroy the edge spin polarization leading to a positive magnetoresistance. This effect provides means to study spin accumulation by electrical measurements. The origin and the general properties of the phenomenological equations describing coupling between charge and spin currents are also discussed.Comment: 4 pages, 3 figures. Minor corrections corresponding to the published versio

Influence of the spin-dependent quasiparticle distribution on the Josephson current through a ferromagnetic weak link

The Josephson current flowing through weak links containing ferromagnetic elements is studied theoretically under the condition that the quasiparticle distribution over energy states in the interlayer is spin-dependent. It is shown that the interplay between the spin-dependent quasiparticle distribution and the triplet superconducting correlations induced by the proximity effect between the superconducting leads and ferromagnetic elements of the interlayer, leads to the appearence of an additional contribution to the Josephson current. This additional contribution $j_t$ can be extracted from the full Josephson current in experiment. The features of the additional supercurrent $j_t$, which are of main physical interest are the following: (i) We propose the experimental setup, where the contributions given by the short-range (SRTC) and long-range (LRTC) components of triplet superconducting correlations in the interlayer can be measured separately. It can be realized on the basis of S/N/F/N/S junction, where the interlayer is composed of two normal metal regions with a spiral ferromagnet layer sandwiched between them. For the case of tunnel junctions the measurement of $j_t$ in such a system can provide direct information about the energy-resolved anomalous Green's function components describing SRTC and LRTC. (ii) In some cases the exchange field-suppressed supercurrent can be not only recovered but also enhanced with respect to its value for non-magnetic junction with the same interface resistances by the presence of spin-dependent quasiparticle distribution. This effect is demonstrated for S/N/S junction with magnetic S/N interfaces. In addition, it is also found that under the considered conditions the dependence of the Josephson current on temperature can be nontrivial: at first the current rises upon temperature increasing and only after that starts to decline.Comment: 19 pages, 9 figures, published version, presentation improve

Radiative Effects in the Standard Model Extension

The possibility of radiative effects induced by the Lorentz and CPT non-invariant interaction term for fermions in the Standard Model Extension is investigated. In particular, electron-positron photo-production and photon emission by electrons and positrons are studied. The rates of these processes are calculated in the Furry picture. It is demonstrated that the rates obtained in the framework of the model adopted strongly depend on the polarization states of the particles involved. As a result, ultra-relativistic particles produced should occupy states with a preferred spin orientation, i.e., photons have the sign of polarization opposite to the sign of the effective potential, while charged particle are preferably in the state with the helicity coinciding with the sign of the effective potential. This leads to evident spatial asymmetries which may have certain consequences observable at high energy accelerators, and in astrophysical and cosmological studies.Comment: 10 pages, 2 figures, Revtex4, to appear in Phys.Rev.D, misprints are correcte

Long range triplet Josephson effect through a ferromagnetic trilayer

We study the Josephson current through a ferromagnetic trilayer, both in the diffusive and clean limits. For colinear (parallel or antiparallel) magnetizations in the layers, the Josephson current is small due to short range proximity effect in superconductor/ferromagnet structures. For non colinear magnetizations, we determine the conditions for the Josephson current to be dominated by another contribution originating from long range triplet proximity effect.Comment: 4 pages, 2 figure

Spin-Hall conductivity of a disordered 2D electron gas with Dresselhaus spin-orbit interaction

The spin-Hall conductivity of a disordered 2D electron gas has been calculated for an arbitrary spin-orbit interaction. We have found that in the diffusive regime of electron transport, in accordance with previous calculations, the dc spin-Hall conductivity of a homogeneous system turns to zero due to impurity scattering when the spin-orbit coupling is represented only by the Rashba interaction. However, when the Dresselhaus interaction is taken into account, the spin-Hall current is not zero. We also considered the spin-Hall currents induced by an inhomogeneous electric field. It is shown that a time dependent electric charge induces a vortex of spin-Hall currents.Comment: 5 pages, figure adde