Transport Properties of Oxide Superconductors and the Influence of Noise on a Modelocked Dynamical System

This thesis is a compilation of two different projects. The first is a series of experimental studies on the high T_{rm c} oxides, while the second is focused on the non-linear dynamics of modelocked systems. The high-T_{rm c} project includes measurements of the tunneling density of states^1 and isotope effect^2 in rm YBa _2Cu_3O_{7-x}, the effect of uniaxial stress on rm YBa_2Cu _3O_{7-x},^3 the anisotropic resistivity, thermoelectric power and thermal conductivity of rm YBa_2Cu_3O _{7-x}^4 and rm Bi_2Sr_2CaCu_2O_8,^ {4-7} and the anisotropic transport of rm Bi_2Sr_2CaCu_2O_8 in the mixed state.^{8,9} The purpose of this research has been three-fold. First, I have set out to measure fundamental superconducting parameters of the high T_{rm c} oxides, such as the energy gap and electron-phonon coupling strength. Second, I have attempted to characterize the normal state by measuring basic electron and phonon transport properties. Lastly, I have investigated how the novel magnetic properties of these materials are manifested in their magnetotransport characteristics. My second major project is a study of the dynamics of modelocked systems in the presence of uncorrelated broadband noise.^{10} By adding white noise to a Josephson junction analog simulator, I and coworkers found that the dynamics of this system is closely described by a noisy circle map, as predicted by Wiesenfeld and Satija.^{11} We have experimentally studied this behavior in different regimes of locking strength.