Spontaneous symmetry-breaking vortex lattice transitions in pure niobium.

Investigation of symmetry-breaking flux-line lattice phases in superconductors by small-angle neutron scattering

In single-crystal superconductors in the mixed state, flux-line structures may have a lower symmetry than the host crystal. In this case, multiple degenerate flux lattice domains may be present simultaneously and give rise to complicated small-angle diffraction patterns. The interpretation of these patterns in terms of the flux lattice structure in a single domain is discussed, with particular ...

Vortices and the Ginzburg - Landau phase transition 1

The methods for studying the role of vortex loops in the phase transition of the Ginzburg-Landau theory of superconductivity using lattice Monte Carlo simulations are discussed. Gauge-invariant observables that measure the properties of the vortex loop distribution are defined. The exact relations between the lattice and continuum quantities make it possible to extrapolate the results of the si...

Structure and degeneracy of vortex lattice domains in pure superconducting niobium: A small-angle neutron scattering study

Berezinski-Kosterlitz-Thouless Transition in Spin Systems

Spontaneous continuous symmetry breaking in two dimensions is not possible for non-zero temperatures. Therefore, common phase transitions are not expected in a two-dimensional xy-model. The appearance of vortices, however, induces the Berezinski-Kosterlitz-Thouless transition. The motivation of this chapter is to derive the arguments for such a transition and investigate some of its properties.

Quantum Phase Transitions in d-wave Superconductors and Antiferromagnetic Kagome Lattices

Strongly correlated systems are of interest due to their exotic collective behavior. In this thesis we study low energy effective theory and quantum phase transitions of d-wave superconductors and spin liquids. First we examine the quantum theory of the spontaneous breaking of lattice rotation symmetry in d-wave superconductors on the square lattice. This is described by a field theory of an Is...