Coupled ferro-antiferromagnetic Heisenberg bilayers investigated by many-body Green's function theory

A theory of coupled ferro- and antiferromagnetic Heisenberg layers is developed within the framework of many-body Green's function theory (GFT) that allows non-collinear magnetic arrangements by introducing sublattice structures. As an example, the coupled ferro- antiferromagnetic (FM-AFM) bilayer is investigated. We compare the results with those of bilayers with purely ferromagnetic or antiferromagnetic couplings. In each case we also show the corresponding results of mean field theory (MFT), in which magnon excitations are completely neglected. There are significant differences between GFT and MFT. A remarkable finding is that for the coupled FM-AFM bilayer the critical temperature decreases with increasing interlayer coupling strength for a simple cubic lattice, whereas the opposite is true for an fcc lattice as well as for MFT for both lattice types.Comment: 17 pages, 6 figures, accepted for publication in J. Phys. Condens. Matter, missing fig.5 adde

Strongly interacting Fermi gases with density imbalance

We consider density-imbalanced Fermi gases of atoms in the strongly interacting, i.e. unitarity, regime. The Bogoliubov-deGennes equations for a trapped superfluid are solved. They take into account the finite size of the system, as well as give rise to both phase separation and FFLO type oscillations in the order parameter. We show how radio-frequency spectroscopy reflects the phase separation, and can provide direct evidence of the FFLO-type oscillations via observing the nodes of the order parameter.Comment: Added one reference. Published in PR

Record dynamics and the observed temperature plateau in the magnetic creep rate of type II superconductors

We use Monte Carlo simulations of a coarse grained three dimensional model to demonstrate that the experimentally observed approximate temperature independence of the magnetic creep rate for a broad range of temperatures may be explained in terms of record dynamics, {\it viz.} the dynamical properties of the times at which a stochastic fluctuating signal establishes records.Comment: 7 pages, 5 figures. Replaced in order to correct the order of the Bessel function in Eq.

KINETIC RESPONSES DURING LANDINGS OF PLYOMETRIC EXERCISES

The objective of the current study was to compare landing impulse and peak ground reaction force (GRF) during a variety of plyometric exercises. Eight Division-I athletes who routinely trained plyometric exercises performed a single repetition each of countermovement jump (CMJ), drop jumps from 30 and 60 cm (DJ30 and DJ60), cone hop (CH), tuck jump (TJ), single leg CMJ (SLJ), and squat jump with 30% 1 RM dumbbell squat (SJ30). Landing impulses and peak GRF were evaluated on an AMTI force plate. One-way ANOVA indicated mean and total impulses and peak GRF differed across exercises, with CH and SLJ displaying lower values and DJ30 and SJ30 having higher values. Results indicate that when landing from various plyometric exercises landing impulses and GRF are different across the exercises

Reaction-diffusion processes and non-perturbative renormalisation group

This paper is devoted to investigating non-equilibrium phase transitions to an absorbing state, which are generically encountered in reaction-diffusion processes. It is a review, based on [Phys. Rev. Lett. 92, 195703; Phys. Rev. Lett. 92, 255703; Phys. Rev. Lett. 95, 100601], of recent progress in this field that has been allowed by a non-perturbative renormalisation group approach. We mainly focus on branching and annihilating random walks and show that their critical properties strongly rely on non-perturbative features and that hence the use of a non-perturbative method turns out to be crucial to get a correct picture of the physics of these models.Comment: 14 pages, submitted to J. Phys. A for the proceedings of the conference 'Renormalization Group 2005', Helsink

Interplay between SDW and induced local moments in URu2Si2

Theoretical model for magnetic ordering in the heavy-fermion metal URu2Si2 is suggested. The 17.5K transition in this material is ascribed to formation of a spin-density wave, which develops due to a partial nesting between electron and hole parts of the Fermi surface and has a negligibly small form-factor. Staggered field in the SDW state induces tiny antiferromagnetic order in the subsystem of localized singlet-singlet levels. Unlike the other models our scenario is based on coexistence of two orderings with the same antiferromagnetic dipole symmetry.The topology of the pressure phase diagram for such a two order parameter model is studied in the framework of the Landau theory. The field dependences of the staggered magnetization and the magnon gap are derived from the microscopic theory and found to be in good quantitative agreement with experiment.Comment: 11 pages, 2 figure