Experimental investigation of the phonon density of states in superconducting thin films, nanowires and nanoparticles

Superconductivity is one of the most intriguing phenomena in solid state physics.  It is characterized by the condensation of electrons into Cooper pairs, i.e. below a particular critical temperature there is an effective attractive interaction between electrons, and in bulk materials this manifests itself in (i) the disappearance of electrical resistance and (ii) the expulsion of an external magnetic field.  This attractive interaction between electrons is mediated via the lattice, and therefore the electron-phonon coupling is essential for superconductivity.  The current challenge in the field, with the rising interest in nanoscale phenomena, is if and how superconductivity can be established when the system size becomes smaller than the typical size of a Cooper pair, a situation occurring in thin films and nanoparticles.

We aim to get a deeper understanding of the intimate link between the overall superconducting properties and the lattice dynamics of nanoscale systems.  We will use synchrotron-based techniques to measure phonons in (ultra) thin films, nanowires and nanoparticles as well as the superconducting gap energy for selected systems. Focusing on low-dimensional systems (films, nanowires and nanoparticles) will allow to gauge the influence of surfaces and interfaces and of finite dimensions on the superconducting properties.  As model systems we will use Nb3Sn films, Sn nanowires and Sn and Pb nanoparticles.