Disappearance of Ensemble-Averaged Josephson Current in Dirty SNS Junctions of d-wave Superconductors

We discuss the Josephson current in superconductor / dirty normal conductor / superconductor junctions, where the superconductors have $d_{x^2-y^2}$ pairing symmetry. The low-temperature behavior of the Josephson current depends on the orientation angle between the crystalline axis and the normal of the junction interface. We show that the ensemble-averaged Josephson current vanishes when the orientation angle is $\pi/4$ and the normal conductor is in the diffusive transport regime. The $d_{x^2-y^2}$-wave pairing symmetry is responsible for this fact.Comment: 8 pages, 5 figure

Influence of thermal fluctuations on quantum phase transitions in one-dimensional disordered systems: Charge density waves and Luttinger liquids

The low temperature phase diagram of 1D weakly disordered quantum systems like charge or spin density waves and Luttinger liquids is studied by a \emph{full finite temperature} renormalization group (RG) calculation. For vanishing quantum fluctuations this approach is amended by an \emph{exact} solution in the case of strong disorder and by a mapping onto the \emph{Burgers equation with noise} in the case of weak disorder, respectively. At \emph{zero} temperature we reproduce the quantum phase transition between a pinned (localized) and an unpinned (delocalized) phase for weak and strong quantum fluctuations, respectively, as found previously by Fukuyama or Giamarchi and Schulz. At \emph{finite} temperatures the localization transition is suppressed: the random potential is wiped out by thermal fluctuations on length scales larger than the thermal de Broglie wave length of the phason excitations. The existence of a zero temperature transition is reflected in a rich cross-over phase diagram of the correlation functions. In particular we find four different scaling regions: a \emph{classical disordered}, a \emph{quantum disordered}, a \emph{quantum critical} and a \emph{thermal} region. The results can be transferred directly to the discussion of the influence of disorder in superfluids. Finally we extend the RG calculation to the treatment of a commensurate lattice potential. Applications to related systems are discussed as well.Comment: 19 pages, 7 figure

The N(p,2π)2NN(p,2\pi)2N reactions near threshold

A preliminary calculation of the total cross sections for the reactions $pn\to pn\pi^+\pi^-$, $pp\to pp\pi^+\pi^-$, $pp\to pp\pi^0\pi^0$, and $pp\to nn\pi^+\pi^+$ was carried out for the incident proton energy range $E_{p}\lesssim 850$ MeV. This calculation was done in the framework of a model based on a version of the standard effective chiral Lagrangian, for which only three- and four-pion diagrams were taken into account together with diagrams containing two two-pion vertices. The invariant amplitudes were calculated to the threshold approximation. It was shown that for a reliable description of the reactions under consideration it is necessary to take into account the $N^*(1440)$ mechanism too. The final state interaction of the nucleons was also considered. Results of the calculation are compared with available experimental data

Low-energy neutron interaction with even-even nuclei and coupled channel optical model

We revised a description of low-energy neutron cross section data for even-even spherical nuclei in terms of the coupled channel optical model (CCOM). It is shown that two-phonon version of this model allows to obtain a unified description of these data assuming slight changes of nuclear diffuseness parameter for magic and near-magic nuclei. Neutron strength functions and scattering lengths for even-even spherical nuclei are also calculated using the same model. Results of these calculations are in a good agreement with experimental data. $N_pN_n$-systematics of inelastic neutron scattering on even-even nuclei is proposed. This systematics combined with CCOM calculations of neutron cross sections presents an additional method for finding nuclei with semimagic numbers of nucleons