Quasiperiodic transition to chaos in Ge; and magnetic susceptibility of high-T(c) superconductors

This thesis consists of the study of two topics in condensed matter physics: nonlinear dynamics in a Ge crystal; and magnetic properties of the high temperature superconductor YBa2Cu3O7. These are given as two parts, each of which can be read independently. The first part is concerned with the measurement of the universal spectrum of scaling indices of the critical attractor of the quasiperiodic route to chaos with golden mean winding number for the helical instability of the electron-hole plasma in a germanium crystal in a magnetic field. The second part consists of measurements of the complex ac magnetic susceptibility of the ceramic superconductor YBa2Cu3O7, and together with theoretical models of the material, assumed to be composed of intergranular junctions and superconducting grains.