This experimental CAREER grant project focuses on the phase diagram describing the flux penetration in Type II superconductors. The discovery by the PI of the solid-liquid transition undergone by the flux lattice in the cuprate superconductors spurs investigation more generally among Type II superconductors of this phase diagram. Of particular interest are the effects that anisotropy, disorder and thermal fluctuations have on creating the newly observed vortex liquid and related states of the Type II superconductor. The experiments will measure the temperature and magnetic field dependencies of the linear and nonlinear resistivities which arise by flux motion. In addition, the critical currents, and energy barriers (activation energies) will be measured. The experimental measurement of flux- flow voltages will cover a very broad voltage dynamic range: sub- picovolt to nanovolt range using a custom-built SQUID-based voltmeter, and from nano to millivolts using state of the art commercial voltmeters. The materials to be studied include both cuprate and conventional layered superconductors. The proposed research will be integrated into an education plan to help enhance student learning and to train future scientists, including members of under-represented minority groups. %%% This CAREER grant project involves fundamental experimental research on the interaction of magnetic fields with the superconducting state. It is focused on the Type II superconductors, which are more tolerant of magnetic field than Type I superconductors, in that magnetic field can penetrate the Type II superconductor in the the form of quantized flux lines or vortices, without necessarily destroying the zero resistance state. Electrical resistance, and therefore heating effects, occur in Type II superconductors when the current density, exerts a sufficiently strong force on the flux lines to cause them to move. This field of research therefore is relevant to the current handling capacity of superconductors in applications involving high currents and high magnetic fields, such as electric power cables and windings in motors or generators. A new phenomenon in this connection, melting or liquid-like motion of the quantized flux lines, has been discovered in the past few years in the high transition temperature cuprate superconductors, which are particularly promising for applications in current carrying cables. The fundamental research carried out in this project therefore is expected to contribute in the long term to an improved electric power technology. The research will be integrated into an education plan to help enhance students learning and to train future scientists, including members of under-represented minority groups. ***
