Nonlocal pseudopotentials and magnetic fields

We show how to describe the coupling of electrons to nonuniform magnetic fields in the framework of the widely used norm-conserving pseudopotential approximation for electronic structure calculations. Our derivation applies to magnetic fields that are smooth on the scale of the core region. The method is validated by application to the calculation of the magnetic susceptibility of molecules within density functional theory (DFT) in the local density approximation. Our results are compared with high-quality all-electron DFT results obtained using Gaussian basis sets and another recently proposed pseudopotential formalism.     

Noncollinear magnetic ordering in a magnetic dimer supported on a metallic substrate

Self-consistent electronic structure calculations for a magnetic dimer supported on a metal surface are performed on the basis of the microscopic Hamiltonian for itinerant electrons. The possibility of a noncollinear ground state in the absence of spin-orbit interaction and magnetic frustration is shown. The effective exchange interaction of moments is determined by the number of quasi-localized d-electrons per atom and, in general, is not described by the Heisenberg model.     

Dynamical electric and magnetic metamaterial response at terahertz frequencies

Utilizing terahertz time domain spectroscopy, we have characterized the electromagnetic response of a planar array of split ring resonators (SRRs) fabricated upon a high resistivity GaAs substrate. The measured frequency dependent magnetic and electric resonances are in excellent agreement with theory and simulation. For two polarizations, the SRRs yield a negative electric response (epsilon < 0). We demonstrate, for the first time, dynamical control of the electrical response of the SRRs through photoexcitation of free carriers in the substrate. An excited carrier density of approximately 4 x 10(16) cm(-3) is sufficient to short the gap of the SRRs, thereby turning off the electric resonance, demonstrating the potential of such structures as terahertz switches. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum.     

Surface modes and multipower-law structure in the early-time electromagnetic response of magnetic targets

It was recently demonstrated [Phys. Rev. Lett. 91, 143908 (2003)] that the scattered electric field from highly conducting targets following a rapidly terminated electromagnetic pulse displays a universal t(-1/2) power law divergence at early time. It is now shown that for strongly permeable targets, micro(c)/micro(b)>1, where micro(b) is the background magnetic permeability, the early-time regime separates into two distinct power law regimes, with the early-early time t(-1/2) behavior crossing over to t(-3/2) at late-early time, reflecting a spectrum of magnetic surface modes. The latter is confirmed by data from ferrous targets where micro(c)/micro(b)=O(10(2)), and for which the early-early-time regime is invisibly narrow.     

Phonon-plasmon modes in a strong magnetic field

Frequencies of phonon-plasmon coupled modes in a strong magnetic field were calculated. The calculations were performed in the long-wave approximation with regard to the electron damping and intrinsic lifetime of optical phonons. The dependence of the Raman scattering cross section on the carrier concentration and the magnetic field intensity was calculated.     

Propagation and radiation characteristics of the circular electric, circular magnetic and hybrid waveguide modes

The field distributions and propagation constants of the circular electric, circular magnetic and hybrid modes of oversized waveguides are expressed, taking the effects of walls into account. These effects are described by wall functions which depend on surface impedances of the wall, and are determined for different types of guides. The near and far field patterns are derived in the case of real wall functions. It is shown that, for very oversized waveguides, the terms containing wall functions can be ignored in the calculations, and it results that the expressions of fields and propagation constants become independent of the types of waveguides. An application to corrugated waveguides for Electron Cyclotron Resonance Heating experiments shows the variations of the radiation characteristics versus geometric parameters of the corrugations and determines the ranges of interest for these parameters.     

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利用离子香蕉轨道中心坐标和香蕉轨道平均算符,讨论了磁岛转动引起的沿磁力线电流分布及其对新经典撕裂模演进的影响.结果显示,考虑此电流的影响,当磁岛旋转频率ω=ω*i时,被离子香蕉轨道宽度效应削弱的自举电流驱动项基本恢复;当ω=ω*e时,离子香蕉轨道宽度效应对自举电流驱动项的削弱则加剧.这意味着磁岛转动方向不同时,此沿力线电流能显著增大或减弱离子香蕉轨道宽度效应对自举电流驱动项的削弱作用.     

小磁岛转动引起的沿磁力线电流对撕裂模的影响

利用离子香蕉轨道中心坐标和香蕉轨道平均算符,讨论了磁岛转动引起的沿磁力线电流分布及其对新经典撕裂模演进的影响。结果显示,考虑此电流的影响,当磁岛旋转频率ω=ω_*i 时,被离子香蕉轨道宽度效应削弱的自举电流驱动项基本恢复;当ω=ω_*e时,离子香蕉轨道宽度效应对自举电流驱动项的削弱则加剧。这意味着磁岛转动方向不同时,此沿力线电流能显著增大或减弱离子香蕉轨道宽度效应对自举电流驱动项的削弱作用。     

Decomposition of silver azide crystals in a constant electric field

New experimental results of investigations of the physicochemical processes initiated in filamentary crystals of silver azide by variously configured electric fields are presented and discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 53–56, October, 2006.     

Dynamics of a dielectric droplet suspended in a magnetic fluid in electric and magnetic fields

The behavior of a microdrop of dielectric liquid suspended in a magnetic fluid and exposed to the action of electric and magnetic fields is studied experimentally. With increasing electric field, the deformation of droplets into oblate ellipsoid, toroid and curved toroid was observed. At the further increase in the electric field, the bursting of droplets was also revealed. The electrorotation of deformed droplets was observed and investigated. The influence of an additional magnetic field on the droplet dynamics was studied. The main features of the droplet dynamics were interpreted and theoretically examined.     

Two-photon interband transitions in semiconductors in a static magnetic field. Nonlocal effects

Summary It is shown that in the presence of a static magnetic field, the electronic states in the effective-mass approximation are described by a Hamiltonian containing a nonlocal potential. In order to preserve the gauge invariance of the transition rates, the interaction between the electrons and the radiation has to be modified. For ZnS, the transition rate between two particular levels is evaluated by showing a difference of more than one order of magnitude when compared with the transition rate previously calculated. Partially supported by the Italian Research Council (C.N.R.) through G.N.S.M.     

Supersolid phase in spin dimer XXZ systems under a magnetic field

Using the quantum Monte Carlo method, we study, under external magnetic fields, the ground state phase diagram of the two-dimensional spin S=1/2 dimer model with an anisotropic intraplane antiferromagnetic coupling. With the anisotropy 4 greater/approximately Delta greater/approximately 3, a supersolid phase characterized by a nonuniform Bose condensate density that breaks translational symmetry is found. The rich phase diagram also contains a checkerboard solid, an antiferromagnet in the z axis, and a superfluid phase formed by S(z)= +1 spin triplets which has a finite staggered magnetization in the in-plane direction. As we show, the model can be realized as a consequence of including the next nearest neighbor coupling among dimers and our results suggest that spin dimer systems may be an ideal model system to study the supersolid phase.     

Localised spin modes of decorated magnetic clusters on a magnetic surface

A method for the calculation of the energies of spin modes of surface magnetic clusters on a magnetic surface, using broken translation symmetry in three dimensions (3D), is employed to determine the spin mode energies for a variety of planar clusters. The cluster is considered to be supported on a magnetically ordered substrate such that the localised spins of the cluster and the substrate interact via magnetic exchange. No electronic effects are considered. The analytical approach solves for the 3D evanescent crystal spin field in the bulk and the surface domains around the cluster. This spin field arises owing to the breakdown of magnetic translation symmetry caused by the surface cluster. The analytical approach can be applied to any cluster configuration, underlying the general character of the calculation. In particular, we consider here a 4-, 5-, and 9-atoms planar clusters supported on the surface of a ferromagnetic simple cubic lattice, the spin order being in the direction normal to surface boundary. The method is applied to calculate the spin mode energies of these planar clusters consisting of Gd atoms interacting via Anti-ferromagnetic exchange with an Fe(1 0 0) surface. These results are compared with the calculated energies of the spin modes of the free clusters, and also with those for the same planar clusters when the cluster-substrate exchange is considered hypothetically ferromagnetic.     

Localized modes of Li and Na impurities in silver halides

The absorption bands due to the infrared-active localized modes of Li and Na substitutional impurity in AgBr and of Li in AgCl are studied at 2 K. The isotope effects of the localized modes are observed in AgBr: Li and AgCl: Li systems. The high frequency sidebands of the Li⁶ localized mode in AgBr are also measured.     

Effect of a change in the optical density of a magnetic emulsion in electric and magnetic fields

The change in the optical density of an emulsion of magnetic fluid drops suspended in a mineral oil under the action of electric and magnetic fields has been investigated. It is found that the sign of the change in transparency in an ac electric field depends on the field frequency. It is shown that, joint action of codirectional low-frequency electric and dc magnetic fields can compensate for the change in the optical density. Calculation of the change in the emulsion optical density within the anomalous diffraction approximation showed that this effect can be explained by small field-induced deformation of microdrops.     

Polariton dynamics of a one-dimensional magnetic photonic crystal in crossed magnetic and electric fields

By an example of a semibounded one-dimensional magnetic photonic crystal (MPC) of easy-axis antiferromagnet-nonmagnetic dielectric type placed in mutually orthogonal dc magnetic and electric fields, conditions are found under which the quadratic magneto-optic interaction leads to a number of anomalies in the reflection and propagation conditions for TM or TE waves incident from outside on the surface of the superlattice. It is assumed that the easy magnetic axis is collinear to the electric field.