Spin Fluctuation Depressed Superconductivity in Nb‐V Alloys

Abstract

The electrical resistivity of Nb-V alloys has been measured around 250 "C. Together with published values of the susceptibility and the electronic part of the specific heat the contribution of spin fluctuations t o the depression of the superconducting transition temperature, T,, has been estimated. A calculation of T, based on experimental resistivity, susceptibility, and specific heat and with one adjustable parameter shows qualitative agreement with the observed T, over the whole alloy system and reasonable quantitative agreement in the dilute B V region. Further evidence for the existence of spin fluctuations in Nb-V and a n enhanced electron-phonon coupling constant L in V is derived from the observed rate of depression of T, with V concentration, published band structure calculations for V, and published Knight shift relaxation times.La rksistivit6 des alliages Nb-V a kt6 determinire aux environs de 250 "C. Avec des valeurs publiees de la susceptibilitk et de la partie 6lectronique de la chaleur spkcifique on a estimk la contribution des fluctuations de spin ti la depression de la temperature de transition, T,. Un calcul de T, A partir de la rksistivitk, la susceptibilitk et la chaleur spkcifique expkrimentales et avec un parametre libre s'accord qualitativement avec la valeur de T, observke dans le systkme d'alliages entier e t est aussi en accord quantitatif raisonable dans la region dilut5e de mT7. Encore d'autre evidence pour l'existence des fluctuations de spin dans Nb-V et pour un couplage klectron-phonon klevk dans le V est obtenu par la depression observee de T , avec la concentration de V, la structure des bandes klectroniques publiees pour V et les temps de relaxation du systbme spin-r8seau.

Weak localization and the Mooij rule in disordered metals

“…(5) to obtain the empirical values of l tr for Nb, Mo, Ta, and W. They found that l tr from resistance and the McMillan's coupling constant l from superconductivity are very similar in magnitude for these materials. We can also mention experimental confirmations by Rapp and Crawfoord [47] for Nb-V alloys, Rapp and Fogelholm [48] for Al-Mg alloys, Flçkiger and Ishikawa [49] for Zr-Nb-Mo alloys, Fogelholm and Rapp [50] for In-Sn alloys, Lutz et al [51] for Nb 3 Ge films, Mankovskii et al [52] for thin Sn films, Rapp et al [53] for Au-Ga alloys, and Sundqvist and Rapp [54] for aluminum under pressure. Figure 3 shows the McMillan's coupling constant l versus dq=dT / l tr for Au-Ga, Au-Al, and Ag-Ga alloys [55], which examplifies the correlation implied by Eq.…”