Vortex dynamics in NbTi films at high frequency and high DC magnetic fields

Area of Science:

• Superconducting Materials Science
• Radiofrequency Engineering
• Condensed Matter Physics

Background:

• Niobium Titanium (NbTi) is a vital superconducting alloy for radiofrequency (RF) applications.
• Understanding vortex dynamics in NbTi films is critical for optimizing RF cavity performance.
• High-frequency characterization techniques are needed to probe these dynamics.

Purpose of the Study:

• To characterize NbTi films at 11 GHz and up to 4 T DC magnetic fields.
• To quantitatively determine penetration depth, complex impedance, and vortex-motion-induced resistivity.
• To analyze vortex-pinning parameters and flux flow resistivity using Campbell penetration depth formalism.

Main Methods:

• Coplanar waveguide resonator technique for RF characterization.
• Analysis of complex impedance within the Campbell penetration depth formalism.
• Comparison with dielectric-loaded resonator technique and other characterization methods.

Main Results:

• Quantitative data on penetration depth, complex impedance, and complex resistivity.
• Determination of vortex-pinning parameters and flux flow resistivity at high frequencies.
• Normalized flux flow resistivity aligns with time-dependent Ginzburg-Landau theory predictions.

Conclusions:

• The study provides a comprehensive understanding of NbTi film electromagnetic properties.
• High-frequency vortex dynamics in NbTi films are well-described by established theories.
• The observed decreasing trend in pinning constant suggests a collective pinning regime.