Title: Probing the Nonlinear Meissner Effect and the Enhancement of the Field Onset of Penetration of Vortices in Dirty Nb Films Under RF and DC Fields
Author: Alex Gurevich
Institution: National High Magnetic Field Laboratory
Abstract: Alex Gurevich
National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32303, USA
The first observation of the nonlinear Meissner effect in dirty Nb films revealed by the measurements of the frequency shift of the Nb thin film 20GHz resonator strip line as a function of the parallel dc magnetic field is reported . The use of films thinner than the London penetration depth has enabled us to circumvent the main obstacle in the observation of the nonlinear Meissner effect due to penetration of vortices. A significant enhancement of the vortex penetration field up to 1T for a 65 nm dirty Nb film is demonstrated. We developed a theory based on the Usadel equations, which describe the experimental data very well. The nonlinear Meissner effect caused by impurities at the surface of Nb cavities can contribute to the medium and high-field Q slope. The thin film strip line resonator method can be very useful for measurements of the surface resistance and the onset of vortex penetration for emerging SRF materials used in thin film coating structures for Nb cavities.
. N. Groll, A. Gurevich, and I. Chiorescu, Phys. Rev. B 81, 020504(R) (2010).