Thermodynamics of anisotropic superconductors

This thesis investigates the thermodynamics of two dimensional and highly anisotropic three dimensional superconductors. The study of these systems requires the ability to measure very small samples, and an experimental apparatus for small sample calorimetry is described.; Specific heat measurements on high quality single crystals of the quasi-two dimensional high temperature superconductor Bi{dollar}sb2{dollar}Sr{dollar}sb2{dollar}Ca{dollar}sb1{dollar}Cu{dollar}sb2{dollar}O{dollar}sb8{dollar} are presented. No evidence for an electronic contribution proportional to temperature is found. Measurements in an applied magnetic field show no signature of a phase transition in the vortex lattice. Measurements of the anisotropic field dependence are shown to be a high precision method for studying the thermodynamics of the superconducting state. There is indirect evidence for a gap in the excitation spectrum in the vortex core. Also, the possibility of using this technique to test for unconventional symmetry of the superconducting order parameter is discussed.; The specific heat of multilayers of superconducting amorphous Mo{dollar}sb{lcub}77{rcub}{dollar}Ge{dollar}sb{lcub}23{rcub}{dollar} layers separated by insulating amorphous germanium is discussed. The multilayers are designed to insure that the superconductivity is effectively two dimensional. The fluctuation regime is found to be in quantitative agreement with predictions for two dimensional superconductivity. The fluctuation peak is rapidly suppressed by the application of small magnetic fields perpendicular to the layers, and the transition becomes extremely broad as the field is increased. The transition widths in large fields scale as expected for a field induced 2D to 0D crossover, and are in excellent agreement with the exact result for 0D fluctuations.; The resistivity, magnetization, and specific heat of the multilayers is compared. The fluctuation magnetization, like the specific heat agrees with the predictions for dimensional crossover. The broadening of the resistive transition is similar to that observed in the specific heat, but is not in quantitative agreement with proposed scaling relations. The resistivity becomes activated immediately below the thermodynamic transition, indicating little or no region describable by conventional flux flow.