International Journal of Modern Physics B

By using a new Hamiltonian,¹ we have calculated the energy of one isolated vortex line and also the interaction energy between the vortices in superconductors. Also, we have calculated the elastic force constant in a vortex lattice. The interaction energy shows a minimum at a certain distance between the vortices. We analyze some aspects of this interaction. The obtained results are in good agreement with experimental data.

Thermal conductivity of MgB₂ at room temperature is measured from the photoacoustic technique and analyzed for electron and lattice contribution to the thermal conductivity in the normal state. These results are compared with the flow cryostat measurements.

The corona poling system for electro-optic polymers with a bias-controlled grid is experimentally studied. The relationship between the corona threshold voltage and the grid bias voltage is researched. There is a minimum in the corona threshold voltage versus grid bias voltage curve. Effects of the grid bias voltage, the mesh size and the grid electrode position on performances of the poling system are discussed and analyzed. The experimental results show that the grid electrode can enlarge the corona discharge dynamic range and control the poling current in a wide range, grid electrodes with different mesh sizes and grid-plate gaps have different effects on performances of the poling system, and the grid electrode should be near the plate electrode to acquire stable corona discharge.

We investigated exact quantum states of the light confined in cubes filled with conductive media whose parameters are explicitly dependent on time and the light propagating under periodic boundary condition by making use of the LR (Lewis–Riesenfeld) invariant operator method. The choice of Coulomb gauge in the charge free space allowed us to evaluate quantized electric and magnetic fields by expanding only the vector potential, since the scalar potential is zero. We also described the fields with a spectrum of continuous mode, which can be obtained by setting the side L to infinity.

A new efficient converging perturbation technique valid for arbitrary interaction strength U/t and electron concentration n is applied to study strongly correlated electrons within the repulsive Hubbard model. We test the new perturbation expansion theory in terms of interacting quasi-particles about generalized self-consistent field (GSCF) solution in an entire parameter space. The developed perturbation formalism for strong interaction and large perturbation region differs from the traditional theory on the vicinity of non-interacting electrons by incorporating systematically fluctuations of quasi-particles around self-consistent solution. Performed analytical calculations of the ground state properties in the extreme conditions of one dimensionality provide quite reasonable numerical agreement with the Bethe-ansatz results in the intermediate range of U/t and n. The results are compared with the predictions of traditional perturbation theory.

We investigate the persistent current in a polyacetylene ring induced by axially symmetric, gauge potentials of both magnetic flux and static electric field using a modified SSH Hamiltonian for the polyacetylene chain. The AB and AC effects for an electron with spin are formulated simultaneously in a completely equal footing. It is shown that the gauge fields result in a Fröhlich-type superconductivity equivalent to the effect of a travelling lattice wave. The total energy as well as the persistent current density are shown to be periodic function of the total effective flux of the both gauge fields of AB and AC embraced by the polyacetylene ring.

Granular Co₃₀Pt₇₀/C and Co₄₅Pt₅₅/C films, consisting of nanoparticle CoPt phases embedded in a carbon matrix, have been made by co-sputtering from CoPt and C targets using a tandem deposition mode. X-ray diffraction shows the existence of hard CoPt phase embedded in an amorphous C matrix after annealing. The coercivities for CoPt/C are strongly dependent on C and Pt composition. Films with coercivity of up to 5.4 kOe and grain size of 7 nm can be obtained. The development of shoulder in hysteresis loop may be contributed to the co-existence of magnetic soft CoPt₃ and hard CoPt phases and the magnetic interactions between them. High remanence M_r/M_s (>0.8) found in our samples indicates the presence of the intergranular interactions in the samples. Observed positive contributions of δm also give evidence of the existence of exchange interaction. High coercivity and large M_r/M_s make granular CoPt/C film with magnetic nanoparticles very attractive for next-generation high-density recording.

The quantum-classical limit together with the associated onset of chaos is employed here in order to illustrate the importance of a proper choice of distance in probability space if one wishes to describe dynamical properties from the information theory viewpoint.

A comparative study is performed on two heterodyne systems of photon detectors expressed in terms of a signal annihilation operator and an image band creation operator called Shapiro–Wagner and Caves' frame, respectively. This approach is based on the introduction of a convenient operator which allows a unified formulation of both cases. For the Shapiro–Wagner scheme, where , quantum phase and amplitude are exactly defined in the context of relative number state (RNS) representation, while a procedure is devised to handle suitably and in a consistent way Caves' framework, characterized by , within the approximate simultaneous measurements of noncommuting variables. In such a case RNS phase and amplitude make sense only approximately.

We study an effective field theory describing cold fermionic atoms near a Feshbach resonance. The effective theory gives a precise description of the dynamics in the limit that the energy of the Feshbach resonance is tuned to be twice that of the Fermi surface. We compute the zero temperature superfluid condensate in this limit, and obtain a critical temperature T_C≃0.43 T_F.