Resistivity Ratio of Niobium Superconducting Cavities

Abstract

Resistivity measurements have been made on Nb cavities, as well as on Pb and Cu, at 296, 77, and 4.2 o K by means of a contactless induced-current method. For superconductors, a constant magnetic field drives the material normal below the transition temperature. These measurements provide a simple means for initial material evaluation as well as a direct means of monitoring the effects of material parameters (purity, heat treatment, gas incorporation, etc.) on the electron mean free path.Approximate determinations of H c , H c1 , and H c2 can also be derived from these measurements. Normal-state thermal conductivity and the Ginzburg-Landau parameter κ are calculated from the resistivity measurements.Measurement of the resistivity ratio (between 296 and 4.2 o K ) of Nb rf superconducting cavities is desirable for many reasons. Resistivity-ratio measurements before and after vacuum firing can indicate the decrease in impurity content and other crystalline defects, as well as measure the increase in the electron mean free path. The latter parameter is important in designing superconducting accelerators and in analyzing the results from superconducting cavities. The effects on the electron mean free path due to irradiation, incorporation of gases, etc., can also be determined. The difficulty in measuring resistivity by ordinary means lies in the size and unwieldy

Measurement of the nonlinear Meissner effect in superconducting Nb films using a resonant microwave cavity: A probe of unconventional pairing symmetries

“…( 2) and ( 7) can be inferred from independent measurements, except the absolute position of the origin ϕ = 0 • relative to the coil axis H 2 . Using the mean-free path extracted from the normal state resistivity, ℓ = ρ −1 × 3.7 pΩcm 2 = 1.6 nm [22], we estimate the dirty limit penetration depth, λ 0 ≃ λ(ξ/ℓ) 1/2 (T c0 /T c ) 1/2 = 226 nm, the coherence length ξ 0 = √ ξℓ(T c0 /T c ) 1/2 = 9 nm, and κ = λ 0 /ξ 0 ≃ 25 for the clean-limit values λ ≃ ξ ≃40 nm [23]. Here the factor T c0 /T c accounts for the difference between our sample critical temperature and T c0 = 9.2 K of pure Nb.…”

Resonant Andreev Spectroscopy in normal-Metal/thin-Ferromagnet/Superconductor Device: Theory and Application

“…The dominating term will depend on the contact dimension a , the resistivity ρ of the sample and the mean free path l of the charge carriers. For ρ = 13 μ Ω cm (as resulting by direct measurements) and considering that ρl = 3.72 × 10 −6 μ Ω cm 2 for niobium 46 47 , it comes out that the minimum contact dimension is a ≃ 8 nm. The ratio l / a < 1 gives indication for diffusive contact.…”

Depth-Resolved Measurements of the Meissner Screening Profile in Surface-Treated Nb

“…This is somewhat lower than the ∼ 810 nm expected for Nb with a residual-resistivity ratio of approximately 300 (see, e.g., Refs. [132,133]); however, we point out that our microscopic method of determining samples only the spatial region probed by the μ + beam, making it more sensitive to the surface region, where, for example, interstitial impurities are likely more prevalent. Similarly, it is at first surprising to find that nonlocal electrodynamics [23,24] are not necessary to describe the data; however, this is consistent with our , which equivalently yields a short "effective" coherence length ξ 0 (at 0 K) according to [116]…”