NSF Award Abstract - #9623306

Vortex Dynamics in Organic and High Temperature Superconductors

Abstract

9623306 Zuo The objective of this proposal is to find the generic features common to both the layered organic and the high temperature superconductors in order to better understand the vortex dynamics in these systems. Several experiments will be performed to this purpose. First, the phenomena of anomalous magnetization where magnetization increases abnormally with increasing field in the mixed state will be studied in both organic and the Thallium based cuprates superconductors where the superconducting transition temperature can be varied. Second, interlayer transport measurements will be performed to correlate with a magnetic transparent state observed in the neodymium-cerium based superconductors as well as the thallium based ones to test the model of the Josephson decoupling between the superconducting layers. Third, a point contact technique will be applied to test a model of spontaneous creations of free vortices due to thermal fluctuations in layered compounds. Fourth, an important phenomena of quantum interference of moving vortex lattice with a rf electromagnetic field will be tested in the organic superconductors. The organics may prove to be an ideal system to establish the quantum interference picture because of its extremely weak pinning. Current voltage response will be measured as a function of flux flow velocity and the rf field. Understanding of the vortex dynamics in the layered superconductors is important for its industrial applications, it is also interesting in terms of fundamental physics. %%% Understanding of the magnetic properties in the high temperature superconductors is critical for applications of these materials as current carrying devices. It is equally interesting in terms of fundamental physics involved. The high transition temperature and the layered structure introduce new features in the behavior of quantum vortices in the mixed state. For example, the magnetization or critical current in the mixed state incre ases abnormally with increasing field. Preliminary studies suggest it is due to dimensional crossover when the quantum vortices changes from 3 dimensional lines to 2 dimensional pancakes. This proposal aims toward establishing a generic picture by comparing the high temperature superconductors with a structurally analogous low temperature organic superconductors. Several key experiments will be performed to test the models proposed for the layered superconductors. These include comparative studies of anomalous magnetization in both systems, direct measurement of coupling between the superconducting layers, detection of spontaneous generated thermal vortices, and an interference effect between the quantum vortices and an incident electromagnetic wave. The knowledge gained from this study will provide better understanding of physics in the mixed state, as well as novel applications of these materials. ***