2,193 research outputs found
Mesoscopic superconductivity in ultrasmall metallic grains
A nano-scale metallic grain (nanoparticle) with irregular boundaries in which
the single-particle dynamics are chaotic is a zero-dimensional system described
by the so-called universal Hamiltonian in the limit of a large number of
electrons. The interaction part of this Hamiltonian includes a superconducting
pairing term and a ferromagnetic exchange term. Spin-orbit scattering breaks
spin symmetry and suppresses the exchange interaction term. Of particular
interest is the fluctuation-dominated regime, typical of the smallest grains in
the experiments, in which the bulk pairing gap is comparable to or smaller than
the single-particle mean-level spacing, and the Bardeen-Cooper-Schrieffer (BCS)
mean-field theory of superconductivity is no longer valid. Here we study the
crossover between the BCS and fluctuation-dominated regimes in two limits. In
the absence of spin-orbit scattering, the pairing and exchange interaction
terms compete with each other. We describe the signatures of this competition
in thermodynamic observables, the heat capacity and spin susceptibility. In the
presence of strong spin-orbit scattering, the exchange interaction term can be
ignored. We discuss how the magnetic-field response of discrete energy levels
in such a nanoparticle is affected by pairing correlations. We identify
signatures of pairing correlations in this response, which are detectable even
in the fluctuation-dominated regime.Comment: 9 pages, 5 figures, Proceedings of the Fourth Conference on Nuclei
and Mesoscopic Physics (NMP14
Magnetic response of energy levels of superconducting nanoparticles with spin-orbit scattering
Discrete energy levels of ultrasmall metallic grains are extracted in
single-electron-tunneling-spectroscopy experiments. We study the response of
these energy levels to an external magnetic field in the presence of both
spin-orbit scattering and pairing correlations. In particular, we investigate
-factors and level curvatures that parametrize, respectively, the linear and
quadratic terms in the magnetic-field dependence of the many-particle energy
levels of the grain. Both of these quantities exhibit level-to-level
fluctuations in the presence of spin-orbit scattering. We show that the
distribution of -factors is not affected by the pairing interaction and that
the distribution of level curvatures is sensitive to pairing correlations even
in the smallest grains in which the pairing gap is smaller than the mean
single-particle level spacing. We propose the level curvature in a magnetic
field as a tool to probe pairing correlations in tunneling spectroscopy
experiments.Comment: 13 pages, 5 figure
Geometric phase shift for detection of gravitational radiation
An effect of geometrical phase shift is predicted for a light beam
propagating in the field of a gravitational wave. Gravitational radiation
detection experiments are proposed using this new effect, the corresponding
estimates being given.Comment: LaTeX2e, 12 p
3,5-Bis(4-chlorobenzylidene)-1-methylpiperidin-4-one
In the title molecule, C20H17Cl2NO, the central heterocyclic ring adopts a flattened boat conformation. The dihedral angles between the planar part of this central heterocyclic ring [maximum deviation = 0.004 (1) Å] and the two almost planar side-chain fragments [maximum deviations = 0.015 (1) and 0.019 (1) Å], that include the aromatic ring and bridging atoms, are 18.1 (1) and 18.0 (1)°. In the crystal, pairs of weak intermolecular C—H⋯O hydrogen bonds link molecules into inversion dimers that form stacks along the a axis. The structure is further stabilized by weak intermolecular C—H⋯π interactions involving the benzene rings
Anomalous Josephson effect in semiconducting nanowires as a signature of the topologically nontrivial phase
We study Josephson junctions made of semiconducting nanowires with Rashba
spin-orbit coupling, where superconducting correlations are induced by the
proximity effect. In the presence of a suitably directed magnetic field, the
system displays the anomalous Josephson effect: a nonzero supercurrent in the
absence of a phase bias between two superconductors. We show that this
anomalous current can be increased significantly by tuning the nanowire into
the helical regime. In particular, in a short junction, a large anomalous
current is a signature for topologically nontrivial superconductivity in the
nanowire.Comment: 10 pages, 9 figures; published versio
1-Benzyl-3,5-bis(4-chlorobenzylidene)piperidin-4-one
The title compound, C26H21Cl2NO, crystallizes with two symmetry-independent molecules (A and B) in the asymmetric unit. In both molecules, the central heterocyclic ring adopts a sofa conformation. The dihedral angles between the planar part of this central heterocyclic ring [maximum deviations of 0.011 (1) and 0.036 (1) Å in molecules A and B, respectively] and the two almost planar [maximum deviations of 0.020 (1) and 0.008 (1) Å in A and 0.007 (1) and 0.011 (1) in B] side-chain fragments that include the aromatic ring and bridging atoms are 20.1 (1) and 31.2 (1)° in molecule A, and 26.4 (1) and 19.6 (1)° in molecule B. The dihedral angles between the planar part of the heterocyclic ring and the benzyl substituent are 79.7 (1) and 53.2 (1)° in molecules A and B, respectively. In the crystal, weak intermolecular C—H⋯O hydrogen bonds link the two independent molecules into dimers
Study of the nuclear component of primary cosmic rays aboard AES ''Proton-2''
Nuclear component of primary cosmic rays aboard Proton II satellite studied with aid of Cherenkov spectromete
- …