Magnetic pair breaking in superconductingBa1−xKxBiO

Abstract

The de Gennes and Maki theory of gapless superconductivity for dirty superconductors is used to interpret the tunneling measurements on the strongly type-II high-T c oxide-superconductor Ba 1−x K x BiO 3 in high magnetic fields up to 30 Tesla. We show that this theory is applicable at all temperatures and in a wide range of magnetic fields starting from 50 percent of the upper critical field B c2 . In this magnetic field range the measured superconducting density of states (DOS) has the simple energy dependence as predicted by de Gennes from which the temperature dependence of the pair-breaking parameter α(T ), or B c2 (T ), has been obtained. The deduced temperature dependence of B c2 (T ) follows the Werthamer-Helfand-Hohenberg prediction for classical type-II superconductors in agreement with our previous direct determination. The amplitudes of the deviations in the DOS depend on the magnetic field via the spatially averaged superconducting order parameter which has a squareroot dependence on the magnetic field. Finally, the second Ginzburg-Landau parameter κ 2 (T ) has been determined from the experimental data.

Type II superconductivity in SrPd2Ge2

“…The electron mean free path was not considered in the estimation of  0 and  0 using only the Fermi velocity, superconducting energy gap and the averaged length of the Fermi contours [22] and concurs with the fact that the effective penetration depth  is much larger than  0 and the effective coherence length  is much smaller than  0 . The notion of the dirty limit is further validated by the applicability of the pair breaking model of de Gennes [35] and Maki [36] to the differential conductance spectra in various magnetic fields (Figure 2 (a)), as described by Szabó et al [37] In this model, the SDOS N(E) of a dirty limit type II superconductor in the gapless region for small  in magnetic fields near B c2 is given by , ) ( 2 (6) where N N (0) is the density of states at the Fermi surface of the superconductor in the normal state and is the Maki -de Gennes pair-breaking parameter.…”

Comparative analysis of tunneling magnetoresistance in low-TcNb/Al-AlOx/Nb and high-TcBiKrasnov1, Motzkau2, Golod3 et al. 2011Phys. Rev. B236500View full textAdd to dashboardCite

“…This was demonstrated in previous studies for cuprates 16,18,[35][36][37] as well as for conventional low-T c (Refs. [38][39][40] and noncuprate 41 high-T c superconductors. Application of magnetic field leads to appearance of a spatially inhomogeneous mixed state.…”

Strong magnetic pair breaking in Mn-substitutedMgB2single crystals

“…24,25 On the other hand, as in conventional superconductors, T c is expected to be affected by the pair-braking effect caused by magnetic impurities or substitutions that suppress superconductivity due to the exchange interaction between conduction elec-trons and magnetic moments of the substituted ions. 26 The magnetic pair-braking effect has been studied intensively in classic 27,28,29,30,31,32,33 and high-temperature superconductors, 34,35,36,37,38 however this effect has remained almost untouched in more exotic superconductors, particularly in two-gap multi-band MgB 2 , where only two reports on such studies has been published. 23,26 The main goal of this work is to study the influence of magnetic Mn-ion substitutions on the normal-state and superconducting properties of high-quality MgB 2 single crystals.…”