A Note on the Metastability of the Ising Model: The Alternate Updating Case

We study the metastable behavior of the two-dimensional Ising model in the case of an alternate updating rule: parallel updating of spins on the even (odd) sublattice are permitted at even (odd) times. We show that although the dynamics is different from the Glauber serial case the typical exit path from the metastable phase remains the same.     

Influence of the sign of the refractive index in the reflectivity of a metamaterial surface with localized roughness

To study the scattering properties of metamaterials, we generalize two scattering methods developed for conventional (non-magnetic) isotropic materials to the case of materials with arbitrary values (positive or negative) of magnetic permeability and electric permittivity. The generalized methods are used to study the changes produced in the reflectivity of a metamaterial surface with localized roughness when the relative refractive index changes sign. Our results show that, unlike the case of a plane surface whose reflectivity is unaffected by the change of sign of the relative refractive index, in rough surfaces the change of sign is manifested in the reflectivity, even for very low roughness, particularly in observation directions away from the specular direction.     

Elliptic critical points: C-points, a-lines, and the sign rule

The critical points of generic paraxial ellipse fields consist of singular points of circular polarization, called C -points, and azimuthal stationary points, i.e., maxima, minima, and saddle points. We define these stationary points here and review their properties. The sign rule for ellipse fields requires that the sign of the singularity indices I(C)=+/-1/2 of the C -points on non-self-intersecting lines of constant azimuthal ellipse orientation (modulo pi/2), i.e., a -lines, alternate along the line. We verify this rule experimentally, using a newly developed interferometric technique to measure C -points and a -lines in an elliptically polarized random optical field.     

On the change in electromagnetic wave polarization in a smooth one-dimensionally inhomogeneous medium

Propagation of an electromagnetic wave in a smooth one-dimensionally inhomogeneous isotropic medium is considered in the second approximation of geometrical optics. The polarization evolution is studied extensively. It is known that in the first (Rytov) approximation of geometrical optics, there is only the rotation of the plane of polarization (with no change in the polarization shape and sign) for rays with torsion. In the case considered, both the shape of polarization ellipse and the sign of polarization change proportionally to the integral of the squared ray curvature even for plane rays. The effect is of nonlocal geometrical nature and can be described in terms of the generalized geometrical phase incursion between two linear polarizations.     

Elementary excitations of topologically disordered systems

We have examined the elementary excitation spectra of continuous random networks having only even rings or both even and odd rings. We have shown that odd rings introduce localized states and suppress the density of states near a spectral bound associated with sign alteration in the spatial dependence of the state. While this is a general conclusion, we show it explicitly only for the nearest-neighbor tight-binding s-band and related magnon and phonon models. In the latter case, phonon softening or phonon hardening can result. In the former case, we show that frustration leads to localized magnons.     

The influence of cascade on the polarization of radiation produced in electronic or atomic collisions

A study is presented, in which we consider the influence of cascade effects on the polarization of light emission produced in electronic or atomic collisions. Cascade transitions are shown to cause a polarization transfer which may result in a total falsification and even in a sign reversal of the polarization. Closed expressions are derived for some special cases. A practical application is given in which the derived formulas are used to understand a serious discrepancy between theoretical predictions and experimental data in the case of the line polarization due to some 3p-3s transitions in neon induced by proton impact.     

Inelastic light scattering by a two-dimensional electron system with Rashba spin-orbit coupling

Inelastic light scattering by a two-dimensional system of electrons in a conduction band with Rashba spinorbit coupling is studied theoretically for the resonance case where the frequencies of the incident and scattered light are close to the effective distance between the conduction band and spin-split band in a III–V semiconductor. It is shown that, in contrast to the case of no spin-orbit coupling, the spectrum of the scattered light exhibits a plasmon peak even for strictly perpendicular polarizations of the incident and scattered light. There exists a configuration where the scattering spectrum exhibits features originating from single-particle transitions only. Furthermore, it is shown that, for the general case of elliptic polarizations of the incident and scattered light, the amplitude of the plasmon peak depends on the sign of the effective Rashba spinorbit coupling constant and the signs of the phases of the polarization vectors. This fact can be used to determine the sign of the Rashba constant.     

Broken even-odd symmetry in self-selection of distances between nanoclusters due to the presence or absence of topological solitons

Depositing particles randomly on a 1D lattice is expected to result in an equal number of particle pairs separated by even or odd lattice units. Unexpectedly, the even-odd symmetry is broken in the self-selection of distances between indium magic-number clusters on a Si(100)-2×1 reconstructed surface. Cluster pairs separated by even units are less abundant because they are linked by silicon atomic chains carrying topological solitons, which induce local strain and create localized electronic states with higher energy. Our findings reveal a unique particle-particle interaction mediated by the presence or absence of topological solitons on alternate lattices.     

On axially-symmetric finite-energy monopole configurations

Axially symmetric finite energy monopole configurations are investigated for the gauge group SO(3) with the Higgs field in the adjoint representation. To avoid the complications due to gauge freedom gauge invariant fields are introduced and used throughout. From topological and continuity considerations it is argued that the only regular axially symmetric magnetic charge distributions permitted are isolated charges of uniform strength and alternate sign located along the axis of symmetry. In particular, if there is only one sign, the magnetic charge must be located at a single point. For a zero Higgs potential the minimal energy (first order Bogomolny) field equations take a simple form when written in terms of the gauge-invariant fields. In general, there are nine equations for nine (axially symmetric) fields, but these reduce to five equations for five fields if a further symmetry (invariance under reflexions in planes through the axis of symmetry) is imposed. Remarkably, four of the equations are the same whether the reflexion symmetry is imposed or not, and these four equations can be completely solved in terms of a master potential. From these and the remaining equations (just one in the case of mirror symmetry) the asymptotic behaviour of the functions at large distances and in the neighbourhood of the origin (the location of the charge) is obtained and studied in some detail.     

The Groundstate of 2-Dimensional Infinite-U Hubbard Model with a Single Hole

The groundstate energies of 1 - and 2-D infinite-U Hubbard models with a single hole are obtained by a simple method. It is found that the groundstates for an arbitrary finite system are multiple degenerate states with S_z = S, S - 1, …, -S (S = (N - 1)/2, N = even is the number of sites). Based on these results, it is shown that the hole and the spin-ffip(s) can not form a bound state, then it provides an alternate proof of Nagaoka's theorem.     

Frequency upshifting of electromagnetic radiation via obliqueincidence on an ionization front

Frequency upshifting of electromagnetic radiation impinging on a relativistically moving ionization front is theoretically investigated. Unlike previous works in this field treating the case of normal incidence and qualitatively similar case of oblique incidence of a transverse electric polarized wave, oblique incidence of a transverse magnetic polarized wave on the front is considered. The peculiarities of the case under consideration are connected with the generation of Langmuir waves behind the front and Brewster's phenomenon. We present a complete analysis of the incident wave transformation including analysis of the frequencies and amplitudes of the waves excited ahead of and behind the front. Special emphasis is made on energy transformation in the case when a wave packet is incident on the front. In particular, we show that even for negligible angles of incidence, energy losses via transformation into Langmuir waves may be very high (up to ~60%). In general, generation of Langmuir waves may play a significant role in the plasma-based radiation sources with relativistic ionization fronts     

Brownian motion in fluctuating periodic potentials

This work deals with the overdamped motion of a particle in a fluctuating one-dimensional periodic potential. If the potential has no inversion symmetry and its fluctuations are asymmetric and correlated in time, a net flow can be generated at finite temperatures. We present results for the stationary current for the case of a piecewise linear potential, especially for potentials being close to the case with inversion symmetry. The aim is to study the stationary current as a function of the potential. Depending on the form of the potential, the current changes sign once or even twice as a function of the correlation time of the potential fluctuations. To explain these current reversals, several mechanisms are proposed. Finally, we discuss to what extent the model is useful to understand the motion of biomolecular motors.     

Spin polarized tunneling at finite bias

A mesoscopic spin valve is used to determine the dynamic spin polarization of electrons tunneling out of and into ferromagnetic (FM) transition metals at finite voltages. The dynamic polarization of electrons tunneling out of the FM slowly decreases with increasing bias but drops faster and even inverts with voltage when electrons tunnel into it. A free-electron model shows that in the former case electrons originate near the Fermi level of the FM with large polarization whereas in the latter, electrons tunnel into hot electron states for which the polarization is significantly reduced. The change in sign is ascribed to the matching of the electron wave function inside and outside the tunnel barrier.     

Charge density of a positively charged vector boson may be negative

The charge density of vector particles, for example W(+/-), may change sign. The effect manifests itself even for a free propagation, when the energy of the W-boson satisfies epsilon>sqrt[2]m and the standing wave is considered. The charge density of W also changes sign in a vicinity of a Coulomb center. For an arbitrary vector boson (e.g., for spin 1 mesons), this effect depends on the g-factor. An origin of this surprising effect is traced to the electric quadrupole moment and spin-orbit interaction of vector particles; their contributions to the current have a polarization nature. The corresponding charge density equals rho(Pol)=-inverted Delta . P, where P is an effective polarization vector that depends on the quadrupole moment and spin-orbit interaction. This density oscillates in space, producing zero contribution to the total charge.     

Giant magnetoresistance in the variable-range hopping regime

We predict the universal power-law dependence of the localization length on the magnetic field in the strongly localized regime. This effect is due to the orbital quantum interference. Physically, this dependence shows up in an anomalously large negative magnetoresistance in the hopping regime. The reason for the universality is that the problem of the electron tunneling in a random media belongs to the same universality class as the directed polymer problem even in the case of wave functions of random sign. We present numerical simulations that prove this conjecture. We discuss the existing experiments that show anomalously large magnetoresistance. We also discuss the role of localized spins in real materials and the spin polarizing effect of the magnetic field.     

An effective approach to same sign top pair production at the LHC and the forward-backward asymmetry at the Tevatron

We study the phenomenology of same sign top pair production at the LHC in a model-independent way. The complete set of dimension six operators involving two top (or anti-top) quarks is introduced and the connection with all possible t- or s-channel heavy particle exchanges is established. Only in the former case, same and opposite sign top pair production can be related. We find that while current Tevatron data disfavor t-channel models, other production mechanisms are viable and can be tested at the LHC.     

Rectification in substituted atomic wires: a theoretical insight

Recently, there have been discussions that the giant diode property found experimentally in diblock molecular junctions could be enhanced by the many-body electron correlation effect beyond the mean field theory. In addition, the effect of electron-phonon scattering on an electric current through the diode molecule, measured by inelastic tunneling spectroscopy (IETS), was found to be symmetric with respect to the voltage sign change even though the current is asymmetric. The reason for this behavior is a matter of speculation. In order to clarify whether or not this feature is limited to organic molecules in the off-resonant tunneling region, we discuss the current asymmetry effect on IETS in the resonant region. We introduced heterogeneous atoms into an atomic wire and found that IETS becomes asymmetric in this substituted atomic wire case. Our conclusion gives the other example of intrinsic differences between organic molecules and metallic wires. While the contribution of electron-phonon scattering to IETS is not affected by the current asymmetry in the former case, it is affected in the latter case. The importance of the contribution of the electron-hole excitation to phonon damping in bringing about the current asymmetry effect in IETS in the latter case is discussed.     

Sign Flip in Giorgi-Pasquale-Paganelli Model

Taking advantage of our improved gates as well as the Giorgi-Pasquale-Paganelli (GPP) nondestructive gate [Phys. Rev. A 70 (2004) 022319], the sign of any term of the initial state in the GPP model can be flipped. The success possibility of the sign flip of odd number of terms is probabilistic (1/4), while the success possibility of the sign flip of even number of terms is deterministic (1).     

Energy levels of QED in a Euclidean formulation

Hydrogen-like energy levels of scalar and spinor QED are calculated using a Euclidean functional approach. The matter field is integrated over. Stationary points of the resulting effective action already yield a hydrogen like level structure for the energy. There is an interesting difference between the scalar and the spinor case. Whereas for spinors the conventional results are reproduced, the calculation for scalars yields a fine structure which is opposite in sign to the conventional one and has no critical singularity at Zα=1/2. The crucial structural difference between the two cases is that, for scalars, minima for the gauge invariant energy are not extrema of the action, even for time independent fields.     

正负折射率材料组成的半无限一维光子晶体的反射率

计算了由正负折射率材料交替生长形成的半无限一维光子晶体的反射率,发现在带隙中,反射率等于1,在通带内,半无限结构的反射率是有限层结构迅速振荡的反射率平均的结果. 当该结构中正负折射率材料的光学厚度相互抵消时,会出现零平均折射率能隙.解析地证明了该结构零平均折射率附近的能隙几乎不随入射角度和偏振情况变化,而且跟晶格常数的标度无关. 关键词： 半无限光子晶体 反射率 负折射率