Impurity band in clean superconducting weak links

Weak impurity scattering produces a narrow band with a finite density of states near the phase difference $\phi =\pi$ in the mid-gap energy spectrum of a macroscopic superconducting weak link. The equivalent distribution of transmission coefficients of various cunducting quantum channels is found.Comment: 4 pages, 4 figures, changed conten

Persistent currents, flux quantization and magnetomotive forces in normal metals and superconductors (Review Article)

The notion of persistent current comes back to orbital currents in normal metals, semiconductors and even insulators displaying diamagnetic behavior in weak magnetic fields, but came to focus at the discovery of current persistence and magnetic flux quantization at large fields in atomically big but macroscopically small (mesoscopic) objects. The phenomenon bears much similarity with supercurrents in superconductive metals. We will review progress in developing of our understanding of the physical and technological aspects of this phenomenon. The exact solution for currents, magnetic moments and magnetomotive forces (torques) in crossed magnetic fields are presented. Time-dependent phenomena in crossed magnetic and electric fields, and in possibility of spontaneous persistent currents and of work extraction from static and dynamic quantum states are discussed

Hopping and correlation effects in atomic clusters and networks

Exact solution for hopping and correlation effects in atomic clusters and mesoscopic/nanoscopic networks is outlined. The program translates the Hamiltonian operator of the cluster written in terms of second-quantized creation and annihilation operators, to sparse matrix of (extremely) large dimension and solves the latter with the help of new compiler termed ABC ("Advanced Basic-C" compiler/converter/programmer). The ABC creates a stand-alone executable or, if proved necessary, source C-code received from the original program written in a simplified Quick Basic dialect. ABC employes mathematical functions including the complex variables, arbitrary precision floating-point numbers, special functions, standard mathematical routines (mulidimensional integrals, eigenvalues of Hermitian marices, in particular a new algorithm for sparce Hermitian matrices, etc.) and is appropriate to practically all software/hardware environments (Windows, OS/2, Linux and UNIX machines)

Non-linear thermoelectricity and cooling effects in metallic constrictions

Linear as well as non-linear contributions to the Zeebeck and Peltier coefficients of a metallic film in contact with the equilibrium metal are calculated within a simple model. The non-linear part of the thermoelectric response survives down to a very low temperature which in principle permits thermoelectric cooling at these conditions. Thermal equilibrium in a metallic constriction between dissimilar metals is evaluated in the non-linear current-carrying regime

Magnetic and electric Aharonov-Bohm effects in nanostructures

The paper reviews and extends the magnetic Aharonov-Bohm effect (persistent current, resistance oscillation) in normal-metal rings including spin-independent and spin-dependent hopping, Zeeman splitting, magnetic textures and wheels, ring rotation and weak coupling, as well as the electric Aharonov-Bohm effect ("persistent charge") in small metallic contacts. We then discuss dynamical screening effects in a surface charge in a metal. Energy dissipation due to motion of the surface charge has a singularity at the velocity of motion equal to the phonon propagation velocity. Surface image of an external charge inside the metal is strongly distorted at the velocity of motion larger than the Fermi velocity

"Transverse" persistent currents in mesoscopic cylinders and rings

Persistent current is a nondecaying current in a normal metal ring or cylinder induced by the vector potential applied parallel to the direction of the current (longitudinal, or Aharonov-Bohm persistent current). A magnetic field applied perpendicular to the wall of the hollow metallic cylinder also produces an azimuthal nondecaying current (a transverse persistent current) even in the absence of the Aharonov-Bohm flux. Magnetic moment of a single connected conductor (a 2d conducting stripe) is supported by a current (a Landau-persistent current) which is shown to oscillate in space. © 2000 Published by Elsevier Science B.V. All rights reserved

Spontaneous and persistent currents in mesoscopic Aharonov-Bohm loops: Static properties and coherent dynamic behavior in crossed electric and magnetic fields

Mesoscopic or macromolecular conducting rings with a fixed number of electrons are shown to support persistent currents due to the Aharonov-Bohm flux, and the "spontaneous" persistent currents without the flux when structural transformation in the ring is blocked by strong coupling to the externally azimuthal-symmetric environment. In the free-standing macromolecular ring, symmetry breaking removes the azimuthal periodicity, which is further restored at the increasing field, however. The dynamics of the Aharonov-Bohm loop in crossed electric and magnetic fields is investigated within the tight-binding approximation; we show that transitions between discrete quantum states occur when static voltage pulses of prescribed duration are applied to the loop. In particular, the three-site ring with one or three electrons is an interesting quantum system that can serve as a qubit (quantum bit of information) and a qugate (quantum logical gate) because in the presence of an externally applied static electric field perpendicular to a magnetic field, the macromolecular ring switches between degenerate ground states mimicking the NOT and Hadamard gates of quantum computers. © 2005 Pleiades Publishing, Inc

Contraction of atomic orbitals in the oxygen anion network and superconductivity in metal oxide compounds

Anion network in the CuO2 plane of metal-oxide compound is considered as an intrinsic-hole metal with holes rather than electrons comprising a Fermi liquid immersed in the background of negative O2- ions. Due to the contraction of p-orbital of oxygen as a result of occupation by a hole, hole hopping between nearest neighbor sites (i, j) is dependent upon hole occupation as tij,σ = to + Vni,-σnj,-σ = W(ni,-σ + nj,-σ). Coupling parameters W and V (additive and multiplicative "contraction interaction" terms) result in the binding of holes into singlet, on-site configuration, or into triplet, nearest-neighbor-site configuration, due to W and V respectively. In the weak coupling limit, W results in the BCS type of superconductive pairing (singlet, s-wave), whereas multiplicative contraction V provides for either singlet, d-wave, or triplet, p-wave-like pairing states. It is concluded that the latter state may result in a plausible mechanism for high-Tc superconductivity in metal oxide compounds. The superconducting p-phase is shown to be in accord with recently published symmetry tests of the order parameter in oxides

Spontaneous and persistent currents in superconductive and mesoscopic structures (Review)

We briefly review aspects of superconductive persistent currents in Josephson junctions of the S/I/S, S/O/S and S/N/S types, focusing on the origin of jumps in the current versus phase dependences, and discuss in more detail the persistent and the "spontaneous" currents in Aharonov-Bohm mesoscopic and nanoscopic (macromolecular) structures. A fixed-number-of-electrons mesoscopic or macromolecular conducting ring is shown to be unstable against structural transformation removing spatial symmetry (in particular, azimuthal periodicity) of its electron-lattice Hamiltonian. In the case when the transformation is blocked by strong coupling to an external azimuthally symmetric environment, the system becomes bistable in its electronic configuration at a certain number of electrons. Under such a condition, the persistent current has a nonzero value even at an (almost) zero applied Aharonov-Bohm flux and results in very high magnetic susceptibility dM/dH at small nonzero fields, followed by an oscillatory dependence at larger fields. We tentatively assume that previously observed oscillatory magnetization in cyclic metallo-organic molecules by Gatteschi et al. can be attributed to persistent currents. If this proves correct, it may present an opportunity for (and, more generally, macromolecular cyclic structures may suggest the possibility of) engineering quantum computational tools based on the Aharonov-Bohm effect in ballistic nanostructures and macromolecular cyclic aggregates. © 2004 American Institute of Physics

Spontaneous and persistent currents in superconductive and mesoscopic structures (Review Article)

We briefly review aspects of superconductive persistent currents in Josephson junctions of the S/I/S, S/O/S and S/N/S types, focusing on the origin of jumps in the current versus phase dependences, and discuss in more detail the persistent as well as «spontaneous» currents in the Aharonov–Bohm mesoscopic and nanoscopic (macromolecular) structures. A fixed-number-of-electrons mesoscopic or macromolecular conducting ring is shown to be unstable against structural transformation removing spatial symmetry (in particular, azimuthal periodicity) of its electron- lattice Hamiltonian. In case when the transformation is blocked by strong coupling to an external azimuthally symmetric environment, the system becomes bistable in its electronic configuration at certain number of electrons. At such a condition, the persistent current has a nonzero value even at the (almost) zero applied Aharonov–Bohm flux, and results in very high magnetic susceptibility dM/dH at small nonzero fields, followed by an oscillatory dependence at larger fields. We tentatively assume that previously observed oscillatory magnetization in cyclic metallo-organic molecules by Gatteschi et al. can be attributed to persistent currents. If this proves correct, it may open an opportunity (and, more generally, macromolecular cyclic structures may suggest the possibility) of engineering quantum computational tools based on the Aharonov–Bohm effect in ballistic nanostructures and macromolecular cyclic aggregates