This is a Focused Research Group (FRG) project which is investigating the perturbation of the d-wave order parameter at interfaces and defects in high temperature, unconventional superconductors. The FRG will investigate the behavior of the superconducting order parameter at surfaces and interfaces by quasiparticle tunneling spectroscopy that can look at the local density of electronic surface states, and by SQUID interferometer measurements capable of determining directly the phase anisotropy that characterizes unconventional superconductors. Thermal conductivity and penetration depth measurements at low temperatures will be used to confirm and characterize the onset of secondary superconductor phases suggested by recent experiments and predicted to occur in doped unconventional superconductors. The FRG will explore the structure of bound and extended vortex states in the vortex core by scanning tunneling microscopy, the only probe with sufficient electronic sensitivity and spatial resolution to map out the structure of the vortex core. A unique magnetic scanning instrument, the scanning Josephson microscope, is being developed to search for the anisotropy of the circulating supercurrents around the vortex, another important feature of vortices in unconventional superconductors. The FRG provides a special environment for training graduate student and postdoctoral research through their involvement in the full spectrum of the project's research topics and techniques %%% This is a Focused Research Group (FRG) project which investigates fundamental questions in the field of high-temperature superconductivity. The collaborative highly integrated structure of the FRG provides and effective approach to this complex problem, allowing a merging of high-quality samples, powerful unique experimental probes, and close interactions with theoretical predications and modeling. It also provides a special environment for training graduate student and postdoctoral research through their involvement in the full spectrum of the project's research topics and techniques. The issues addressed here are of great interest and importance in condensed matter physics because of their relevance to the growing list of superconductors confirmed to be unconventional (cuprate, heavy fermion, organic, ruthenate, bobocarbide, etc.) and to the general subject of highly correlated electron systems. ***
