Speaker
Description
We present a study of the normal-state and superconducting properties of thin-film $\mathrm{Nb_{1-x}Ti_{x}N}$ using depth-resolved $^8$Li $\beta$-detected nuclear magnetic resonance ($\beta$-NMR). Spin-polarized $^8$Li$^{+}$ ions were implanted ~21 nm into a Nb$_{0.75}$Ti$_{0.25}$N(91 nm)/AlN(4 nm)/Nb sample, with their NMR response recorded at temperatures between 4.6 K to 270 K under a 4.1 T field applied normal to the film surface. The resonance spectra exhibit broad, symmetric lineshapes at all temperatures, with additional broadening observed below the superconducting transition temperature $T_\text{c} \approx 15$ K attributed to vortex lattice formation. Lineshape broadening analysis yields the film's magnetic penetration depth $\lambda$ and upper critical field $B_\mathrm{c2}$, whose values are in good agreement with literature estimates. Spin-lattice relaxation (SLR) data reveal Korringa behavior at low temperatures, with thermally activated dynamics dominated above ~100 K. Below $T_\mathrm{c}$, a small Hebel-Slichter coherence peak is observed, characterized by a 2.60 meV superconducting energy gap and modest Dynes-like broadening, consistent with strong-coupling superconductivity. These results provide a foundation for future studies of the Meissner-to-vortex transition in Nb$_{0.75}$Ti$_{0.25}$N/AlN/Nb heterostructures, which is relevant for next-generation Nb superconducting radiofrequency (SRF) cavities (common components of particle accelerators).
| asadm@uvic.ca | |
| Supervisors Name | Tobias Junginger |
| Supervisors Email | junginger@uvic.ca |
