Superconducting plate in a transverse magnetic field: New state

A model is proposed for describing Cooper pairs near the transition (in temperature and magnetic field) point when their spacing is larger than their size. The essence of the model is as follows: the Ginzburg-Landau functional is written in operator form in terms of field operators of the Bose type so that the average value of the density operator gives the concentration of Cooper pairs, and the same Ginzburg-Landau expression is obtained for the Bose condensate. The model is applied to a superconducting plate with a thickness smaller than the size of a pair in a transverse magnetic field near its upper critical value H _c2. A new state is discovered that is energetically more advantageous in a certain interval in the vicinity of the transition point as compared to the Abrikosov vortex state. The wavefunction of the system in this state is of the type of the Laughlin function used in the fractional quantum Hall effect (naturally, as applied to Cooper pairs as Bose particles in our case) and corresponds to a homogeneous incompressible fluid. The energy of this state is proportional to the first power of quantity (1 ? H/H _c2) in contrast to the energy of the vortex state containing the square of this quantity. The interval of the existence of the new state is the larger, the dirtier the sample.     

Robustness of Greenberger-Horne-Zeilinger and W states for teleportation in external environments

By solving analytically a master equation in the Lindblad form, we study quantum teleportation of the one-qubit state under the influence of different surrounding environments, and compared the robustness between Greenberger-Horne-Zeilinger (GHZ) and W states in terms of their teleportation capacity. The results revealed that when subject to zero temperature environment, the GHZ state is always more robust than the W state, while the reverse situation occurs when the channel is subject to infinite temperature or dephasing environment.     

Anomalous thermoelectric power of rare earth metals and their compounds

We propose a new mechanism for an anomalous thermoelectric power (ATP) in the paramagnetic state of certain rare earth metals and their compounds, in which the ions possess a nonmagnetic ground state in a given crystal field. The ATP is found to be due to higher order inelastic scattering (second Born approximation) of the conduction electrons by the crystal field split rare earth ions. It has a peak at a temperatureΔ/3 ~Δ/2, whereΔ is the splitting energy between the ground state and the first excited state. Our main result is that the appearance of an ATP requires interactions between the conduction electrons and the ions of other than the simple isotropic exchange type. This implies that the ATP may serve as a valuable tool to detect more complicated types of thek-f interaction than the isotropic exchange.     

Quantum state sharing of an arbitrary m-qudit state with two-qudit entanglements and generalized Bell-state measurements

A scheme for quantum state sharing of an arbitrary m-qudit state is proposed with two-qudit entanglements and generalized Bell-state (GBS) measurements. In this scheme, the sender Alice should perform m two-particle GBS measurements on her 2m qudits, and the controllers also take GBS measurements on their qudits and transfer their quantum information to the receiver with entanglement swapping if the agents cooperate. We discuss two topological structures for this quantum state sharing scheme, a dispersive one and a circular one. The former is better at the aspect of security than the latter as it requires the number of the agents who should cooperate for recovering the quantum secret larger than the other one.     

Revival of metastable behavior in phase separated La0.5Ca0.5MnO3+δ

The La_xCa_1−xMnO_3+δ compositions close to charge ordering (x∼0.5) show a gradual relaxation from a metallic/ferromagnetic state to an insulating/antiferromagnetic state with thermal cycling. Here, we report on the magnetic relaxation in the metastable state and also the revival of the metastable state (in a relaxed sample) due to high temperature thermal treatment. We also show the changes in the magnetization and the thermoelectric power as the revived metastable state is cycled. We find that the changes in the thermoelectric power extend well into the region above the charge ordering temperatures. This suggests that the micro-structural changes accompanying the thermal cycling leave their imprint in the paramagnetic insulating state as well.     

Complex motion in nonlinear-map model of elevators in energy-saving traffic

We have studied the dynamic behavior and dynamic transitions of elevators in a system for reducing energy consumption. We present a nonlinear-map model for the dynamics of M elevators. The motion of elevators depends on the loading parameter and their number M. The dependence of the fixed points on the loading parameter is derived. The dynamic transitions occur at 2(M−1) stages with increasing the value of loading parameter. At the dynamic transition point, the motion of elevators changes from a stable state to an unstable state and vice versa. The elevators display periodic motions with various periods in the unstable state. In the unstable state, the number of riding passengers fluctuates in a complex manner over various trips.     

Nuclear hyperfine interactions in spherical top molecules

The nuclear hyperfine Hamiltonian for XY₄ and XY₆ spherical top molecules in their ground electronic state is built up by a tensor method, and is given by a linear combination of invariant tensor products in the group ^L0(3) × G(G = T_d or 0_h); the case when an external magnetic field is applied is also considered. For the study of a given vibrational state, the appropriate restriction is easily determined; as examples were consider the ground vibronic state and a triply degenerate fundamental state.     

Resonant excitation of a new valence state in N2 by electron impact

A new valence state which lies below the first Rydberg state has been observed in N₂, in the 11.3 to 12.1 eV energy range, using an electron impact technique. This state is only excited from 1.3 to ～3 eV above its threshold through a short lived resonance. Some levels are not clearly resolved but their presence is deduced from the resonant profiles of their differential cross sections. A perturbation in the relative intensities of the C³Π_u vibrational levels is observed when this new state is excited.     

Simultaneous electron-photon excitation of hydrogen and helium

Total and differential cross sections for simultaneous excitation of H(2s), H(3s) and He(1s 2s) by electron impact in the presence of a photon field have been calculated in second-order perturbation theory. The characteristics of the results are interpreted in terms of their physical origin. The off-shell excitation cross section for the He(1s 2s) state is found to be one order of magnitude smaller than that for excitation of the H(2s) state. This is consistent with our expection that atoms with higher dipole-polarisability should favour larger off-shell cross sections for transitions betweens-states.     

Unitary transformation treatment of a single hole in an Ising antiferromagnet

The behavior of a single hole in a two-dimensional Ising antiferromagnet (t-J ^z model), is studied in the generalized Dyson-Maleev representation, where the spins are mapped on boson operators and the hole is described as a spinless fermion. The formal similarity with Fröhlich's polaron Hamiltonian suggests that thet-J ^z model can be approximately diagonalized by means of two successive unitary transformations, analogous to those used by Lee, Low, and Pines in their intermediate-coupling treatment of the polaron. Our approach yields an upper bound to the exact ground state energy, as well as the corresponding ground state eigenvector. Fork=0 our energy bound is remarkably close to the result of the self-consistent Born approximation over a wide range of the coupling parameter, which includes the range typically assumed for the high-T _c materials. The ground state eigenvector is used to calculate the spatial distribution of bosons (spin deviations) surrounding the hole. Here our results are qualitatively very similar to those obtained in previous work, showing that our ground state eigenvector accounts quite well for the small size of the “spin polaron” in thet-J ^z model.     

Unitary representations of non-compact supergroups

We give a general theory for the construction of oscillator-like unitary irreducible representations (UIRs) of non-compact supergroups in a super Fock space. This construction applies to all non-compact supergroupsG whose coset spaceG/K with respect to their maximal compact subsupergroupK is “Hermitean supersymmetric”. We illustrate our method with the example of SU(m, p/n+q) by giving its oscillator-like UIRs in a “particle state” basis as well as “supercoherent state basis”. The same class of UIRs can also be realized over the “super Hilbert spaces” of holomorphic functions of aZ variable labelling the coherent states.     

Interaction of a moving dipole with a soliton in the KdV equation

The Korteweg-de Vries equation with the perturbing term εδ'(x −Vt) (a point-like dipole), which models disturbances produced by a small body moving in a liquid layer, is considered. In the case V<0, when the moving dipole emits a quasi-linear monochromatic wave, perturbation of the emission spectrum due to collision of the dipole with a free soliton is investigated. It is demonstrated that prior to the collision (at ft → − ∞) the resultant spectrum's width is exponentially small in ∣t∣, while after the collision (at t → + ∞) the width is ∾t⁻¹. Then it is demonstrated that in the case V>0 (a non-emitting dipole) a soliton may be pinned by the moving dipole. In the adiabatic approximation, the pinned state is stable provided ε < 0. In this case a pair of solitons may also be pinned by the dipole, but that pinned state is unstable. Other types of solitary pinned profiles and their stability are discussed. Oscillations of a soliton near the adiabatically stable pinned state are accompanied by emission of quasi-linear waves. The emission intensity is calculated in a general form, and it is demonstrated that the oscillation are subject to radiative instability due to the fact that the energy of the system is not positive definite. The same model is considered with the Bürgers' dissipative term. The dissipation may compensate the radiative instability and render the pinned state of a soliton completely stable. Besides, it is demonstrated that the Bürgers' term gives rise to multisoliton pinned profiles. A maximum possible number of solitons in the profile is found.     

Direct observation of the critical state in low-κ type-II superconductors

New results on the properties of niobium and vanadium in the mixed state obtained by the neutron depolarization method are presented. Magnetization measurements were taken on several samples differing in their degree of hysteresis to obtain the characteristic fieldsH _c1,H ⁺ andH _c2 (H ⁺ denotes the field where the major hysteresis loop for one sense joins the initial magnetization curve). The depolarization is always observed to begin atH _c1 and to disappear atH ⁺. A theoretical reexamination of the critical state concept for low-κ type-II superconductors leads to the conclusion that the maximum depolarization indicates the entrance of the entire sample into the critical state. The actual value of the depolarization is shown to be a measure of the flux line lattice distortions. Furthermore, evidence for an anisotropic flux density distribution in the mixed state is presented.     

J/Ψ suppression in relativistic heavy ion collisions through final state interactions with excited nucleons

TheJ/Ψ suppression in relativistic heavy ion collisions through final state interactions with excited state nucleons is estimated in a manner analogous to that of Gerschel and Hüfner for ground state nucleons. If excited state nucleons are larger in size than nucleons in their ground state, theJ/Ψ absorption cross section is increased. Because of relativistic time dilation this effect does not significantly alter theJ/Ψ suppression previously found.     

Liquid–gas and other unusual thermal phase transitions in some large-N magnets

Much insight into the low temperature properties of quantum magnets has been gained by generalizing them to symmetry groups of order N, and then studying the large-N limit. In this paper we consider an unusual aspect of their finite temperature behavior—their exhibiting a phase transition between a perfectly paramagnetic state and a paramagnetic state with a finite correlation length at N=∞. We analyze this phenomenon in some detail in the large “spin” (classical) limit of the SU(N) ferromagnet which is also a lattice discretization of the CP^N−1 model. We show that at N=∞ the order of the transition is governed by lattice connectivity. At finite values of N, the transition goes away in one or less dimension but survives on many lattices in two dimensions and higher, for sufficiently large N. The latter conclusion contradicts a recent conjecture of Sokal and Starinets [Nucl. Phys. B 601 (2001) 425], yet is consistent with the known finite temperature behavior of the SU(2) case. We also report closely related first order paramagnet–ferromagnet transitions at large N and shed light on a violation of Elitzur's theorem at infinite N via the large-q limit of the q state Potts model, reformulated as an Ising gauge theory.     

Pecularities of EPR spectra of the Gd impurity in the Sn-Rich Pb1−x Sn x Te(Gd) solid solutions

An electron paramagnetic resonance (EPR) experimental study of crystalline and powder p-Pb_1?x?y Sn _y Gd _y Te samples for various matrix compositionx and Gd contenty has been carried out. The study reveals that grinding the crystals into powder as well as their low-temperature annealing turns Gd impurity ions from the EPR-silent Gd²⁺ state to the EPR-active Gd³⁺ state, whereas high-temperature annealing in vacuum quenches EPR signals from Gd³⁺ ions. The experimental results are interpreted in terms of a model assuming that the trivalent charge state of the Gd impurity ions in lead and tin tellurides is a component part of the “substituting Gd impurity-Te vacancy” complex.     

New polaronic excitons in ferroelectric oxides: phenomenological theory

It is shown that three types of new polaronic excitons exist in ferroelectric oxides-charge transfer vibronic excitons (CTVEs). The electron-hole bipolaron pairs are common in all these cases, the difference having to do with the origin of charge transfer-lattice instabilities. These are the cases of the charge transfer and lattice distortions and their vibronic interactions induced in the harmonic (i) and anharmonic (ii) regimes both in the electronic excited state on the one hand, and the (iii) case of the CTVE excited vibronic state induced in the anharmonic regime but related with electronic ground state on the other. All these CTVEs are characterized by strong coupling with good self-localization conditions in separate orientation wells of their multi-well potentials. The relevant phenomenological theory is developed. While the (i) type CTVE is confirmed by luminescence experiments, the (iii) type CTVE with low excitation energy and with metastable intrinsic defect behaviour can be a candidate for the explanation of an order-disorder effect in the classical ferroelectric oxides discovered recently [Phys. Rev. Lett. 90 (2003) 037601].     

Spatial periphery of lithium and beryllium isotopes

The spatial structure of the periphery of lithium and beryllium isotopes is studied by means of charge-exchange reactions and the (t, p) and (d, p) reactions on their nuclei. It is shown that the 0⁺ isobaric-analog state of ⁶Li at 3.56 MeV has a halo structure formed by a proton and a neutron, that there is virtually no manifestation of a neutron halo in the ground state of the ⁹Li nucleus, and that the ¹¹Li nucleus has a Borromean halo structure that two neutrons form with respect to the ⁹Li core and which manifests itself in cigar and dineutron configurations. The ¹⁰Be nucleus has a substantial two-neutron periphery in either configuration both in the ground and in the 2⁺ excited state at 3.37MeV.     

Quantum-networks: master equation and local measurements

Based on the SU(n)-algebra the Markoff master equation in discrete product space is reformulated to explicitly deal with composite systems. The resulting local (single node) and nonlocal (multi-node) state parameters allow a systematic approach to non-classical features of the state, like variance and covariance tensors. For local optical driving forces, inter-node interactions, and local damping channels the solution of the master equation is unraveled into stochastic quantum trajectories. Sampling leads to a joint distribution function in terms of those state parameters. Its linear moments define the ensemble-density matrix. The average variance and covariance are in terms of non-linear moments, which should be distinguished from their entirely statistical counterpairs. Non-classicality of the network dynamics is shown to reflect itself in the luminescence-photonstatistics.