Kondo correlations and the Fano effect in closed Aharonov-Bohm interferometers

We study the Fano-Kondo effect in a closed Aharonov-Bohm (AB) interferometer which contains a single-level quantum dot and predict a frequency doubling of the AB oscillations as a signature of Kondo-correlated states. Using the Keldysh formalism, the Friedel sum rule, and the numerical renormalization group, we calculate the exact zero-temperature linear conductance G as a function of the AB phase phi and level position epsilon. In the unitary limit, G(phi) reaches its maximum 2e(2)/h at phi = pi/2. We find a Fano-suppressed Kondo plateau for G(epsilon) similar to recent experiments.     

Empirical pairing gaps and neutron-proton correlations

Analysis of various mass formulas related to neutron-proton correlations in atomic nuclei is carried out.Using the example of the N =Z chain it is shown that for self-adjoint nuclei various formulas proposed in literature for estimating the np pairing energy lead to similar results. Significant differences between the calculation methods arise when nuclei with N = Z are considered, which allows to reveal the complexity of neutron-proton correlations in different types of atomic nuclei and to make assumptions on the correspondence of the mass relation to the real effect of np pairing. The Shell Model parametrization of the binding energy makes it possible to draw additional conclusions on the structure of mass formulas and their relationship.     

Aharonov-Bohm effect revisited

The Aharonov-Bohm (AB) effect shows that electromagnetic potentials can influence an electron in a field-free region. The single-slit and double-slit electron diffraction patterns are explicitly calculated here by the Feynman path integral method for different configurations of the magnetic field in order to compare the effect of the vector potential with the effect of the magnetic field. When an electron passes through a magnetic field behind the slits, the whole diffrection pattern is shifted due to the Lorentz force. When an electron passes through two slits with magnetic flux confined to a small cylinder between them, the double-slit diffraction pattern is shifted within the single-slit diffraction envelope. The asymmetric diffraction pattern corresponds to a nonzero average displacement and momentum of the electron even though the field exerts no force on the electron. This behavior can be understood on the basis of a quantum-mechanical interference effect. The classical limit of the electron diffraction patterns is taken to obtain the classical particle distributions. The effect of the potential vanishes in the classical limit, while the effect of the magnetic field persists because of the Lorentz force.     

Spatial correlations of pairing collective states

The properties of the low-energy nuclear spectrum are greatly affected by pairing correlations. We study these effects in the nucleus ²¹⁰Pb which has two particles moving outside closed shells. The configuration-mixed wave functions describe the motion of particles which are on the average closer together than they would be if the particles were confined to particular orbitals. Since the energy associated with pairing correlations is much smaller than the Fermi energy the width of the associated probability distribution is determined by the wavelength of single particles moving close to the Fermi surface. Despite the fact that the amplitudes associated with high-lying configurations are small, their net effect is important, typically changing the collectivity of the states by a factor of about two. The results of the microscopic calculations compare well with a semiclassical pairing transition density calculated on the basis of the Thomas-Fermi approximation.     

The optical Aharonov-Bohm effect

It is shown that the vector potential of a circularly polarized laser causes the optical equivalent of the Aharonov-Bohm effect. An estimate is made of the expected fringe shift due to a circularly polarized laser directed through an optical fiber in an electron diffraction experiment, and it is shown that the effect is equivalent to that of a magnetic field.     

Strong hyperon-nucleon pairing in neutron stars

We explore the possibilities of hyperon-nucleon pairing, involving lambda or sigma- hyperons, using different Nijmegen hyperon-nucleon potentials. We find possible very large nsigma- gaps and estimate their relevance for neutron star physics.     

The effect of neutron-proton pairing correlations on the transfer of a neutron-proton pair

A theory of neutron-proton pairing interaction is developed considering bothJ=0T=1 andJ≠0T=0 correlations. The model of a singlej-shell is investigated explicitly forN=Z nuclei. Instead of solving the full HFB (Hartree Fock Bogoliubov) problem a variational method is used for determining the ground state energy and wavefunction. Our model shows that the best solutions contain either onlyT=0 or onlyT=1 correlations. A solution mixingT=0 andT=1 is energetically worse. It is estimated in PWBA (Plane Wave Born Approximation) that for ground state transitions at light nuclei in the transfer of a neutron-proton pair the cross section is enhanced up to a factor 3 by pairing correlations compared with shell model calculations.     

Dyon condensation and the Aharonov-Bohm effect

We derive the string representation of the Abelian Higgs theory in which dyons are condensed. It happens that in such a representation the topological interaction exists in the expectation value of the Wilson loop. Due to this interaction the dynamics of the string spanned on the Wilson loop is nontrivial. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 367–371 (25 March 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Aharonov-Bohm effect in spherical billiard

Using Gutzwiller's periodic orbit theory, we study the quantum level density of a spherical billiard in the presence of a magnetic flux line added at its center, especially discuss the influence of the magnetic flux strength on the quantum level density. The Fourier transformed quantum level density of this system has allowed direct comparison between peaks in the level density and the length of the periodic orbits. For particular magnetic flux strength, the amplitude of the peaks in the level density decreased and some of the peaks disappeared. This result suggests that Aharonov-Bohm effect manifests itself through the cancellation of periodic orbits. This phenomenon will provide a new experimental testing ground for exploring Aharonov-Bohm effect.     

Interplay of pairing and quadrupole correlations in deformed nuclei

We study pairing correlations in deformed nuclei in the framework of the Nilsson+BCS theory. As in the spherical case, the pairing interaction is found to induce strong spacial correlations between the partners of each paired couple. The presence of the deformed mean field gives rise to a non-spherical pair field, whose deformation is governed by the properties of a few single-particle orbitals around the Fermi surface and does not necessarily follow the shape of the mean field. Multipole expansion of the pair field yields all the pair densities associated with the direct two-particle transfer processes to the members of the g.s. rotational band in the A+2 system. The interplay of the deformations of the mean and the pair fields can lead to different relative magnitudes and phases of these densities and therefore to different excitation patterns of the rotational bands in two-particle transfer reactions. In the case of non-collective twoquasiparticles and bands the associated pair densities display large components with high multipoles and the associated transfer processes may be favoured in heavy-ion collisions by kinematical conditions. Examples corresponding to both prolate and oblate cases are considered.     

Conservation laws and the electric Aharonov-Bohm effect

The original derivation of the electric Aharonov-Bohm effect is analysed. It is shown that the operation of a simple device based upon the principles used in that derivation is incompatible with the law of energy conservation. It is concluded that the original proof of the effect is incorrect.     

Particle-number fluctuation of pairing correlations for Dy isotopes

Within the relativistic mean field(RMF) theory, the ground state properties of dysprosium isotopes are studied using the shell-model-like approach(SLAP), in which pairing correlations are treated with particlenumber conservation, and the Pauli blocking effects are taken into account exactly. For comparison, calculations of the Bardeen–Cooper–Schrieffer(BCS) model with the RMF are also performed. It is found that the RMF+SLAP calculation results, as well as the RMF+BCS ones, reproduce the experimental binding energies and one- and twoneutron separation energies quite well. However, the RMF+BCS calculations give larger pairing energies than those obtained by the RMF+SLAP calculations, in particular for nuclei near the proton and neutron drip lines. This deviation is discussed in terms of the BCS particle-number fluctuation, which leads to the sizable deviation of pairing energies between the RMF+BCS and RMF+SLAP models, where the fluctuation of the particle number is eliminated automatically.     

Study of weak pairing correlations in aluminum nanograins

Weak pairing correlations in aluminum nanograins have been investigated using a symmetrical polynomial method based on the wave functions projected onto states with a fixed number of electrons. It is shown that this approach does not lead to a sharp transition from the superconducting to normal state with an increase in temperature, and the intensity of the pairing correlations exceeds that obtained using traditional BCS theory.     

Macroscopic test of the Aharonov-Bohm effect

The Aharonov-Bohm (AB) effect is a purely quantum mechanical effect. The original (classified as type-I) AB-phase shift exists in experimental conditions where the electromagnetic fields and forces are zero. It is the absence of forces that makes the AB effect entirely quantum mechanical. Although the AB-phase shift has been demonstrated unambiguously, the absence of forces in type-I AB effects has never been shown. Here, we report the observation of the absence of time delays associated with forces of the magnitude needed to explain the AB-phase shift for a macroscopic system.     

Classical origins of the Aharonov-Bohm effect

It is shown, in a large variety of manifestations, that the Aharonov—Bohm effect has classical counterparts in aspects concerning energy and momentum balance. No counterexamples are found in the cases considered, although whenever image charges shield the magnetic field region from the electric field of the passing electron the classical momentum effects, while present, would not be observable. Similarly, if the magnetic flux is maintained by superconductors, magnetic shielding will also render the classical energy effect unobservable. Partial shieldings of either type will reduce but not totally eliminate the corresponding observable classical manifestations of these effects.