Supercurrent determined from the Aharonov-Bohm effect in mesoscopic superconducting rings

We have solved the Bogoliubov-de Gennes equation for a clean, one-dimensional mesoscopic superconducting ring threaded by a magnetic flux Φ. We show that the superfluid velocity is driven directly by Φ while the relative motion of the pair of electrons is independent of Φ. Meanwhile, the fluxoid quantization is obtained straightforwardly. More importantly, we have also calculated the supercurrent numerically and self-consistently and find it is periodic in Φ with the period Φshc/2e for Φs≤Φd=(mvdL/ Latin small letter h with strokeπ)Φs and with the period Φ0hc/e for Φd<Φs, which arises from mesoscopic effects. © 1994 The American Physical Society.published_or_final_versio

Self-sustained Aharonov-Bohm flux in mesoscopic rings: Continuum hard-core boson model

We perform analytical calculations to study the persistent current I of a q-charged hard-core boson gas in mesoscopic rings enclosing a magnetic flux , and find that this current is periodic in with the period 0=hc/q. More interestingly, in the presence of a single -function impurity, it has been found that there generally exists a spontaneous Aharonov-Bohm flux as long as the current-induced flux is included. © 1995 The American Physical Society.published_or_final_versio

Topological effects associated with fractional statistics in one-dimensional mesoscopic rings

Using both the continuum and tight-binding models, we have investigated analytically the etfects of a statistical phase factor on the persistent charge and magnetic moment currents of "free" hard-core anyons in one-dimensional mesoscopic rings. In particular, we find that the ground state of the system could, in most cases, self-sustain the Aharonov-Bohm and Aharonov-Casher effects simultaneously.published_or_final_versio

Spontaneous Aharonov-Casher effect of neutral hard-core bosons in one-dimensional mesoscopic rings

Using a tight-binding model Hamiltonian and applying the Jordan-Wigner transformation, we have investigated the Aharonov-Casher (AC) effect for many neutral hard-core bosons in one-dimensional (1D) mesoscopic rings with the self-induced AC phase included. The total energy and the persistent fluxon current are analytically derived for 1D perfect lattices. More importantly, it is suggested that, in the absence of the external AC flux, the self-sustained AC flux state could be the ground state of a system with weak disorder. The possibility of experimenal observations is briefly discussed. © 1995 The American Physical Society.published_or_final_versio

Magnetic scattering effects on quantum transport in a normal-metal–superconductor junction

Within a scattering formalism, the magnetic scattering effects on the transport properties of a normal metal attached to a d-wave as well as an s-wave superconductor have been studied by inserting (i) a Kondo-like magnetic barrier and (ii) a ferromagnetic scattering layer into the normal conducting region. It is shown that, in contrary to our intuition, the Kondo-like magnetic scattering effect is quite similar to the effect of nonmagnetic scattering. Remarkably, the ferromagnetic exchange interaction could lead to the strong resemblance of the conductance behavior between a normal-metal–s-wave superconductor junction containing a ferromagnet layer and a normal-metal–d-wave superconductor with a nonmagnetic scattering layer, and vice versa. This result may complicate significantly the decisive determination of the pairing symmetry in high-Tc superconductors by the quasiparticle tunneling into the superconductor. In addition, the resonance peak splitting in the conductance is exhibited if the ferromagnet layer is located several superconducting coherence lengths away from the normal-metal–superconductor interface.published_or_final_versio

Effects of geometric Berry phase on persistent currents in large-U one-dimensional Hubbard rings

By using the Bethe-Yang ansatz within the framework of the tight-binding model, the ground-state energy and the pesistent current in one-dimensional Hubbard rings are calculated in the presence of an AB flux accompanied by a local magnetic field whose direction varies in space. Analytical result are obtained for large-U limit. It is indicated that there usaually exists no short periodicity for the ground-state energy and persistent current due to the effect of the geometric Berry phase even for the case of infinite U. In a special case, the short periodicity retained in the zero-order approximation is broken down by taking into account the first-order energy correction for large but not infinite U. Moreover, it is found that in the strong-coupling limit, the electron-electron interaction suppresses the persistent current, which is in agreement with other numerical calculations. © 1995 The American Physical Society.published_or_final_versio

Resonant tunneling of holes in double-barrier structures in the presence of an in-plane magnetic field

Using the asymptotic transfer-matrix method, we investigate me resonant tunneling of holes in double-barrier semiconductor structures in the presence of an in-plane magnetic field. The transmission coefficients including ll (light to light hole), hl (light to heavy hole), hh (heavy to heavy hole), and lh (heavy to light hote) are calculated as a function of energy. As in the case of nonzero parallel wave vectors, the mixing of note tunneling can also occur due to the in-plane magnetic field. Moreover, as has been observed by resonant magnetotunneling spectroscopy, we also find that the different resonances have quite different magnetic-field dependences. © 1996 American Institute of Physics.published_or_final_versio

Supercurrent and quasiparticle interference between two d-wave superconductors coupled by a normal metal or insulator

In the presence of an elastic barrier at both interfaces of a mesoscopic d-wave superconductor-normalmetal-d-wave superconductor (DND junction), the Josephson current at zero temperature is studied by using a simple matrix method. As a limiting case, the tunneling between two d-wave superconductors coupled by a insulator barrier (DID structure) is particularly addressed. The effects of sign change and anisotropic gap structure of the d x2-y2 superconductor are carefully considered in the Andreev reflection. The coupling of forward-moving quasiparticles and backward-moving quasiparticles with different pair potentials leads to contrasting Andreev spectra in different motion angle regions, which is specific to our model. Unlike conventional superconducting point-contact junctions, the conduction crossing the Fermi surface plays an important role in determining the critical current. Our theoritical results suggest that the dependence of the critical current on the grain boundary tilt angle provides a clue to identify the pairing symmetry of high-T c. superconductors.published_or_final_versio

Bound states and Josephson current in mesoscopic s-wave superconductor–normal-metal–d-wave superconductor junctions

We have investigated the superconducting phase difference dependence of Andreev levels and Josephson current through a mesoscopic normal-metal layer in contact with two superconducting electrodes with s-wave and d-wave pairing symmetry (SsNSd junction). It is shown that, regardless of the junction length, due to the sign change of the d-wave order parameter under suitable arrangements, the zero-energy point of Andreev levels for the negative process appears at Φ=0. In particular, at zero temperature, the amplitude of the total Josephson current through the point contact SsNSd junction could be enhanced by the sign change of the d-wave order parameter. However, for an SsNSd junction of special length, the amplitude of Josephson current may be suppressed by this sign change. Moreover, as a special case, the midgap surface states discovered by Hu [Phys. Rev. Lett. 72, 1526 (1994)] are recovered naturally. © 1996 The American Physical Society.published_or_final_versio

A general method for designing the transformer of flyback converters based on nonlinear FEA of electromagnetic field coupled with external circuit

This paper presents a general method for designing the transformer of flyback switching AC-DC converters based on nonlinear finite element analysis (FEA) of electromagnetic field coupled with external circuit. For that, the variation patterns of the PWM duty ratio and the current flowing through the windings of transformer versus the input voltage are introduced first, and then several important principles for the design of the transformer are given by using analytical method. As the magnetic saturation and control delay possess heavy influence on the safety of the operation, a MATLAB/Simulink based simulation model, in which both the nonlinear differential inductance and the control delay are included, is built to predict the converter transient performance. The nonlinear differential inductance is calculated by a general program of nonlinear 2-D FEA in Matlab/Simulink surrounding. By running the model, the performances of the converter with different loads and input voltages are obtained. Simulation results are in good agreement with theoretical analysis