November 8th
when: Thursday 8/11/2018, 10:30
where: KE E-541 (møterom)
speaker: Rasmus Toft-Petersen (Technical University of Denmark)
title: Vortex glasses of magnetic flux in Type-II superconductors
abstract:
In the so-called Type-II superconductors, magnetic flux can penetrate the superconducting condensate above a critical field, in the form of a lattice of quantized flux lines. Applying a carrier current to the superconductor drives the lattice to move, dissipating heat. To prevent this, impurities is introduced in the superconducting material, that serve as ‘pins’, holding the lattice in place in a metastable configuration. Since the resulting lattice configuration, and the corresponding degree of order, has a direct impact on the critical current of the superconductor, an understanding of the effects of pinning on this elastic vortex lattice is essential.
In our work, we have investigated the properties of the so-called ‘Bragg glass’ phase of vortex matter, using Small Angle Neutron Scattering (SANS). Quasi-long-range order characterizes the Bragg glass, producing diffraction peaks in a neutron scattering experiment. As the applied field is increased, the properties of the Bragg glass changes. The correlation length drops rapidly at a critical field, signifying the loss of long-range order along with the Bragg peaks it produces. Interestingly, this transition to a ‘vortex glass’ has no impact on the critical current of our sample. This observation sheds light on the hypothesis that the loss of long-range order in the vortex lattice cause a peak in the critical current, suggesting that less ordered static lattice configuration may not be as significant for the critical current as previously thought.