engleski

Microwave response of thin niobium films under perpendicular static magnetic fields

The microwave response of high quality niobium films in a perpendicular static magnetic field has been investigated. The complex frequency shift was measured up to the upper critical fields. The data have been analyzed by the effective conductivity model for the type-II superconductors in the mixed state. Thin niobium films can serve as model system for the upper critical field determination of high-$\kappa$ superconducting samples from microwave measurements. The depinning frequency of the thinnest (10\:nm) film is $\approx 20\:\rm{; ; ; ; ; ; ; GHz}; ; ; ; ; ; ; $ due to the surface pinning centers. For samples with high values of depinning frequency, one should measure both components of the complex frequency shift in order to determine the flow resistivity.

Nb thin films ; upper critical fields ; microwave response

cond-mat/0602168