Magnetic pair-breaking in superconducting (Ba,K)BiO_3 investigated by magnetotunneling

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-Tc oxide-superconductor Ba1-xKxBiO3 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 Bc2. 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 alpha(T), or Bc2(T), has been obtained. The deduced temperature dependence of Bc2(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 square-root dependence on the magnetic field. Finally, the second Ginzburg-Landau parameter kappa2(T) has been determined from the experimental data.

11 pages, 5 figures

References in corpus (4)

• Upper critical field pecularities of superconducting YNi2B2C and LuNi2B2C
• Tunneling measurements of the electron-phonon interaction in $\mathrm{B}{\mathrm{a}}_{1-\mathrm{x}}{\mathrm{K}}_{\mathrm{x}}\mathrm{Bi}{\mathrm{O}}_3$
• Upper critical field in {Ba${}_{1-x}$K${}_x$BiO${}_3$}: magnetotransport versus magnetotunneling
• Superconducting energy gap in $\mathrm{B}{\mathrm{a}}_{1-\mathrm{x}}{\mathrm{K}}_{\mathrm{x}}\mathrm{Bi}{\mathrm{O}}_3$: Temperature dependence

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• 3D-2D crossover in the naturally layered superconductor (LaSe)1.14(NbSe2)
• Comparative analysis of tunneling magnetoresistance in low-$T_c$ Nb/AlAlOx/Nb and high-$T_c$ Bi${}_{2-y}$Pb${}_y$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ intrinsic Josephson junctions
• Type II superconductivity in SrPd2Ge2
• Two-gap superconductivity in the noncentrosymmetric La${}_3$Se${}_4$ compound