Francesco Tafuri: Macroscopic Quantum Effects and mesoscopic fingerprints in High-Tc Superconductor systems and nanostructures

Francesco Tafuri CNR-INFM- Coherentia and Seconda Università di Napoli, ITALY Macroscopic Quantum Effects and mesoscopic fingerprints in High-Tc Superconductor systems and nanostructures The nature of superconductivity in oxide compounds is a very intriguing and still unsolved problem. The phenomenology of high critical temperature superconductors (HTS) encompasses a wide range of interesting issues at the border of our understanding of solid-state systems and at the limit of material science and nano-technology current capabilities. The complexity of these materials, the extreme values of their characteristic lengths and energies, the possibility to tune their order and their properties through the oxygen content are crucial ingredients for a composite and complicated phenomenology. Josephson junctions represent privileged systems to study quantum processes including macroscopic quantum effects. In HTS a d-wave order parameter symmetry (OPS) gives additional elements of interest related for instance to dissipation mechanisms due to mid-gap states, nodal quasi-particles. We will report on recent experiments on YBa2Cu3O7 biepitaxial grain boundary (GB) Josephson junctions and nanostructures. In Josephson junctions the possibility to tune d-wave effects through a suitable geometry has been proved, opening some perspectives for novel device concepts and quantum circuitry. We will discuss the occurrence of macroscopic quantum effects and energy level quantization in a d-wave Josephson junction The results indicate that the role of dissipation mechanisms in HTS has to be revised. This is of great importance for a unique class of solid state “quiet” quantum bit. Mesoscopic fingerprints have been retraced in the properties of HTS submicron junctions and nanostructures, whose realization has been made possible by the steady improvements in the realization and handling of HTS thin films accompanied by the impressive progress in nanotechnologies. The ambitious integration of HTS nanostructures in quantum circuits is only the first direct target. The possibility to have reproducible and reliable HTS nanostructures is also a major contribution towards nanoscale experiments, able to have access to the extremely small characteristic length scales and to contribute to a better identification of basic features of HTS. Confirmé par PF.