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Microwave Vortex Motion Characterization of Nb$_3$Sn Coatings for Applications in High Magnetic Fields

Pablo Vidal García, Andrea Alimenti, Dorothea Fonnesu, Davide Ford, Alessandro Magalotti, Giovanni Marconato, Cristian Pira, Sam Posen, Enrico Silva, Kostiantyn Torokhtii, Nicola Pompeo

Abstract

In this work, microwave measurements carried out in dielectric-loaded resonators exposed to high magnetic fields are exploited to yield the surface impedance of Nb$_3$Sn superconducting coatings deposited via two different techniques: vapor tin diffusion, and DC magnetron sputtering. The obtained data lead to qualitative interpretations on both the Nb$_3$Sn superconducting properties, and vortex-dynamics and pinning, of each coating separately, as well as simple distinctive features when comparing those. When examining the respective surface impedances at varying field, it is expected that the studied films perform at substantially diverse magnitudes of flux-flow resistivity, but also in well-differentiated pinning regimes, yet the obtained surface resistances of both samples are comparable, thus demonstrating that there is room for film optimization at the expense of certain compromise between the parameters involved.

Microwave Vortex Motion Characterization of Nb$_3$Sn Coatings for Applications in High Magnetic Fields

Abstract

In this work, microwave measurements carried out in dielectric-loaded resonators exposed to high magnetic fields are exploited to yield the surface impedance of NbSn superconducting coatings deposited via two different techniques: vapor tin diffusion, and DC magnetron sputtering. The obtained data lead to qualitative interpretations on both the NbSn superconducting properties, and vortex-dynamics and pinning, of each coating separately, as well as simple distinctive features when comparing those. When examining the respective surface impedances at varying field, it is expected that the studied films perform at substantially diverse magnitudes of flux-flow resistivity, but also in well-differentiated pinning regimes, yet the obtained surface resistances of both samples are comparable, thus demonstrating that there is room for film optimization at the expense of certain compromise between the parameters involved.
Paper Structure (7 sections, 5 equations, 3 figures)

This paper contains 7 sections, 5 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Theoretical background
  3. Measurement methods
  4. Results
  5. Temperature sweeps
  6. Field sweeps
  7. Conclusion

Figures (3)

  • Figure 1: $Q_0$ and $\Delta\nu_0$ concerning the measurements of the VTD and DCMS samples as a function of the applied magnetic field, at $\nu_{0}\approx8.50\,\textrm{GHz}$ and $\nu_{0}\approx8.25\,\textrm{GHz}$, respectively, both measured at $T\approx6\,\textrm{K}$.
  • Figure 2: Surface resistance variation of VTD and DCMS samples as a function of temperature ($\Delta R_s(T)$), at zero field. The vertical dashed lines indicate $T_c$, whereas the horizontal dotted lines mark the normal state surface resistance ($R_s\simeq\Delta R_s$). In the inset, the top view of the open DR ($\diameter25\,\textrm{mm}$) with the DCMS sample mounted within is shown. The small dielectric rutile rests on top, which is covered with a thin PTFE cap used as spacer to adjust the coupling. The magnetic field is applied perpendicular to the base of the resonator and sample. The same mounting is used for the VTD sample.
  • Figure 3: Surface impedance variation of the VTD and DCMS sample as a function of the applied magnetic field ($\Delta Z_s(H)$), at $T\approx\,6\,\textrm{K}$. In the inset, the complex plane associated to $\Delta Z_s$ is represented to outline the differences between the samples' response (see discussion thereof in Section \ref{['sec:H-sw']}).