High frequency relaxation kinetics in metal and high-Tc superconductor nanocontacts

The presented work deals with an interesting and relatively simple experimental method, called Point Contact Spectroscopy that permits to study the behaviour of quasiparticles (phonons) in conductive solids: their generation, interactions with electrons, disappearance. We could investigate by this technique also more exotic processes for other quasiparticles (conduction electrons), such as their trapping in a semi metal crystal lattice (Sb), the pairing in superconducting solids, and the absorption of phonons by electrons. Point Contact Spectroscopy consists in the creation of a nanocontact (10-100 nm in diameter) between two conductors and in monitoring its response to electromagnetic fields. When kept in liquid helium, an enormous current density in the range of 109 A/cm2 can be created in such a constriction and in these conditions, the contact becomes an instrument for revealing the quantum properties of electrons and phonons.