2025/05/20 by Asaduzzaman, Md, McFadden, Ryan M. L., Thoeng, Edward +10
#FOS: Physical sciences #Superconductivity (cond-mat.supr-con)
paper · doi:10.48550/arxiv.2505.14591
We report measurements of the normal-state and superconducting properties of thin-film \mathrmNb1-xTixN using 8Li β-detected nuclear magnetic resonance (β-NMR). In these experiments, radioactive 8Li+ probes were implanted ∼21 nm below the surface of a \mathrmNb1-xTixN(91 nm) film in \mathrmNb0.75Ti0.25N(91 nm)/AlN(4 nm)/Nb and its NMR response recorded (via 8Li's β-emissions) between 4.6 K and 270 K in a 4.1 T field applied normal to its surface. Resonance measurements reveal wide, symmetric lineshapes at all temperatures, with significant additional broadening below the film's superconducting transition temperature Tc(0 T) = 15.4 ± 0.7 K due to vortex lattice formation. Fits to a broadening model find a magnetic penetration depth λ(0 K)= 180.57 ± 0.30 nm and upper critical field Bc2(0 K)= 18 ± 4 T, consistent with literature estimates. Spin-lattice relaxation (SLR) measurements find a Korringa response at low temperatures, with dynamic (i.e., thermally activated) contributions dominating above ∼100 K. Below Tc, we observe a small Hebel-Slichter coherence peak characterized by a superconducting energy gap Δ(0 K) = 2.60 ± 0.12 meV and modest Dynes-like broadening. Our measurements suggest a gap ratio 2Δ(0 K)/kBTc(0 T) = 3.92 ± 0.25, consistent with strong-coupling behavior. Sources for the dynamic high-T relaxation are suggested.