Short wavelength fluctuation effects on the magnetization in type I and low-κ typeII superconductors

Abstract

The effects on the magnetization of fluctuating Cooper pairs created above thesuperconducting transition by thermal agitation energy (the so-calledfluctuation-induced diamagnetism, FD) have been measured in a clean type Isuperconductor (Pb) and in a clean low Ginzburg–Landau parameter (κ)type II superconductor (Nb). These experiments extend the earliermeasurements of Gollub, Beasley and Tinkham to both the high reducedtemperature region (ε ≡ ln (T/TC0) ≳ 0.1)and the high reduced magnetic field region (h ≡ H/HC2 (0) ≳ 0.1).Our data show that in spite of FD being deeply affected in bothsuperconductors by the presence of non-local electrodynamic effects,the superconducting fluctuations sharply vanish when ε orhbecome of the order of 0.5 and, respectively, 1. This short-wavelengthbehaviour at high reduced temperatures of the superconducting fluctuations issimilar to that previously observed at high reduced temperatures in dirtylow-TC superconductorsand in high-TCcuprates, where the non-local effects are unobservable. These last results suggestthat in the short wavelength regime the superconducting fluctuations in cleanlow-TCsuperconductors are still dominated by the uncertainty principle,which imposes a limit to the shrinkage, when εincreases, of the superconducting wavefunction. This may also be the case when h → 1,although the presence of strong non-local effects in these clean and low-κsuperconductors may also deeply affect their high field behaviour.