The science of useful superconductors - and beyond

Improved methods of depositing thin film composites embodying transition metals have opened opportunities for finding out more about transition metal superconductors. Results from many research groups are reviewed. In order to reach higher transition temperatures with A-15 structures it will be necessary to synthesize them as ordered structures with more metastable compositions. An interesting dependence of the critical currents upon resistivity of A-15 superconductors has been found. Some indication of the temperature dependence of phase boundaries at low temperatures is discussed. The bottleneck in tunneling into transition metals due to the lack of well-behaved barriers has been broken. Superconducting tunneling spectroscopy has given new insights into the stability of high transition temperature superconductors with the A-15; an important role of impurity gases such as oxygen has been demonstrated. Composites consisting of very fine-scaled multilayered films can be synthesized and show crossover and other interesting behavior when the period is reduced below 50Å.