The College of William and Mary, Williamsburg, USA
JLAB, Newport News, Virginia, USA
Superconducting thin films and multilayers have attracted the attention of the scientific community due to the promise of overcoming the maximum field gradients that SRF cavities can withstand, pushing them above 100 MeV/m *. Nevertheless, in order to achieve the desired properties, special attention needs to be devoted to the epitaxy and growth mode of such thin films, taking into account multiple aspects such as crystalline quality, lattice strain, grain size, etc. We present a complete correlation between morphology, structure and superconducting properties such as critical field, critical temperature and complex susceptibility for single crystal Nb(110) thin films sputter deposited on a-plane sapphire substrates. The influence of strain and grain boundaries in the superconducting transition is analyzed in detail, since the lattice mismatch between Nb and sapphire induces strain in the first atomic layers and may affect the superconducting properties of the thin films. AC susceptibility techniques allow us to identify the dissipative effects in the lattice associated with the presence of defects, thus allowing us to tune the growth conditions to minimize their effect.
*A. Gurevich, Applied Physics Letters 88 (1), 012511 (2006).
