Examination of the peak in dI_CO/dlntin weak-linked highT_csuperconductors caused by trapped flux

Abstract

Altshuler et al discovered that dICO/dlnt, the rate of increase of the critical current IC with time in polycrystalline high TC samples, traced a peak when measured versus HM, the amplitude of the sweep of the flux trapping magnetic field. We show that the sharp peak in dICO/dlnt which their model generates arises from a special feature of the formulae they use to describe IC versus HM. Pursuing an extension of these formulae, and exploiting a Brandt–Indenbom formula for the return field of the magnetized grains, we (i) reproduce observations of Altshuler et al, Batista-Leyva et al and a family of curves of dICO/dlnt reported by Cobas et al, and (ii) estimate the return fields. We also explore the peak structure of dICO/dlnt versus HM generated by using two well known empirical expressions for IC(H), and the Brandt–Indenbom formula.