Электрические и магнитные свойства нанонитей Pb и In в асбесте в области сверхпроводящего перехода

Bulk nanocomposites based on superconducting metals Pb and In embedded into matrices of natural chrysotile asbestos with the nanotube internal diameter d ~ 6 nm have been fabricated and studied. The low-temperature electrical and magnetic properties of the nanocomposites demonstrate the superconducting transition with the transition critical temperature T _c ≈ (7.18 ± 0.02) K for the Pb–asbestos nanocomposite (this temperature is close to T _c bulk = 7.196 K for bulk Pb). The electrical measurements show that In nanofilaments in asbestos have T _c ~ 3.5–3.6 K that is higher than T _c bulk = 3.41 K for bulk In. It is shown that the temperature smearing of the superconducting transition in the temperature dependences of the resistance R ( T ) Δ T ≈ 0.06 K for the Pb–asbestos and Δ T ≈ 1.8 K for the In–asbestos are adequately described by the fluctuation Aslamazov–Larkin and Langer–Ambegaokar theories. The resistive measurements show that the critical magnetic fields of the nanofilaments extrapolated to T = 0 K are H _ c (0) ~ 47 kOe for Pb in asbestos and H _ c (0) ~ 1.5 kOe for In in asbestos; these values are significantly higher than the values for the bulk materials ( H $$H_{\rm{c}}^{\rm{bulk}}$$ H c b u l k = 803 Oe for Pb and $$H_{\rm{c}}^{\rm{bulk}}$$ H c b u l k = 285 Oe for In). The results of the electrical measurements for Pb‒asbestos and In–asbestos agree with the data for the magnetic-field dependences of the magnetic moment in these nanocomposites.