Non-Gaussianity in three fluid curvaton model

The generation of non-gaussianity is studied in a three fluid curvaton model. By utilizing second order perturbation theory we derive general formulae for the large scale temperature fluctuation and non-gaussianity parameter, $f_{NL}$, that includes the possibility of a non-adiabatic final state. In the adiabatic limit we recover previously known results. The results are applied to a three fluid curvaton model where the curvaton decays into radiation and matter. We find that the amount of non-gaussianity decreases as the final state of the system becomes more adiabatic and that the generated non-gaussianity in the scenario is small, $|f_{NL}| \sim \mathcal{O}(1)$.Comment: 10 pages, 2 figure

Gunn diodes and devices (bibliography for 1978-1980)

A listing of about 500 works from Soviet and foreign scientific literature on Gunn diodes and devices based on them is presented. The bibliography includes publications in which various questions pertinent to all (or several) types of semiconductor instruments in the superhigh frequency range are mentioned. A subject index is included

Electromagnon excitations in modulated multiferroics

The phenomenological theory of ferroelectricity in spiral magnets presented in [M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006)] is generalized to describe consistently states with both uniform and modulated-in-space ferroelectric polarizations. A key point in this description is the symmetric part of the magnetoelectric coupling since, although being irrelevant for the uniform component, it plays an essential role for the non-uniform part of the polarization. We illustrate this importance in generic examples of modulated magnetic systems: longitudinal and transverse spin-density wave states and planar cycloidal phase. We show that even in the cases with no uniform ferroelectricity induced, polarization correlation functions follow to the soft magnetic behavior of the system due to the magnetoelectric effect. Our results can be easily generalized for more complicated types of magnetic ordering, and the applications may concern various natural and artificial systems in condensed matter physics (e.g., magnon properties could be extracted from dynamic dielectric response measurements).Comment: 5 page

Domain enhanced interlayer coupling in ferroelectric/paraelectric superlattices

We investigate the ferroelectric phase transition and domain formation in a periodic superlattice consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. We find that the polarization domains formed in the different FE layers can interact with each other via the PE layers. By coupling the electrostatic equations with those obtained by minimizing the Ginzburg-Landau functional we calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layer superlattices.Comment: Latest version as was published in PR

Magnetic Phase Transitions in the NdFe_3(BO_3)_4 multiferroic

Low temperature studies of the behavior of the sound velocity and attenuation of acoustic modes have been performed on a single crystal NdFe_3(BO_3)_4. Transitions of the magnetic subsystem to the antiferromagnetically ordered state at T_N \approx 30.6 K have been revealed in the temperature behavior of the elastic characteristics. The features in the temperature behavior of elastic characteristics of the neodymium ferroborate and its behavior in the external magnetic field, applied in the basic plane of the crystal, permit us to suppose that the transition to an incommensurate spiral phase is realized in the system. This phase transition behaves as the first order one. H-T phase diagrams for the cases H \parallel a and H \parallel b have been constructed. The phenomenological theory, which explains observed features, has been developed