We study the phase diagram of flux lines in superconductors with columnar pins. Based on numerical exact diagonalization simulations on small clusters, we get two phases of vortices: A low-temperature pinned glass with diverging tilt modulus and a high-temperature delocalized entangled vortex liquid. For random potential disorder we find a new phase transition temperature T BG from a pinned Bose glass to an entangled liquid that reduces with increasing vortex density. This occurs primarily because vortices screen the disorder potential and generate an effective weaker random potential with increasing vortex density. For a fixed fraction of randomly placed attractive columnar pins, we find a Mott-insulating phase when the vortex density exactly matches the density of pins at the matching field BϭB . We also find a transition from a strongly pinned Bose glass for BϽB to a weakly pinned Bose glass for BϾB as the vortex density is varied.

No abstract

We study, using numerical exact diagonalisation, some static and dynamical properties of a single impurity substituted into a one-dimensional repulsive Hubbard chain. A systematic scan of the parameter-space reveals a rich magnetic phase diagram. Interactions on the lattice stabilize the local moment phase of the impurity. A scalar impurity is seen to induce local moments on the neighbouring sites near Half Filling. Static spin and charge correlation functions reflect a non-Fermi liquid character of the ground state in the presence of a scalar impurity.