We investigate properties of unconventional novel superconducting materials, such as the high-Tc cuprates and Sr2RuO4 in restricted geometries. We also studied the unconventional ordering induced in nanoscale superconductor-ferromagnet heterostructures. Long-range order in these materials is affected either by the physical size of a sample or by contact to other materials. This gives rise to new physics that governs Josephson transport, current-voltage characteristics, heat conduction, and, in the case of superconductor-ferromagnet structures, local spin polarization.
To have a proper description of ultra-small superconducting systems, one needs to know the quasi-particle density of states, which is usually strongly modified compared to its bulk-material value due to quantum interference effects. These interference effects occur when the size of the system is comparable to the superconducting coherence length (approximately 1-100 nm). Moreover, in unconventional superconductors with an anisotropic pairing state of the Cooper pairs, these interference effects are intrinsic and always present because of non-homogeneities, such as surfaces, interfaces, or impurities.