Nonexponential London penetration depth of external magnetic fields in superconducting Ba1−xKxFe2As2 single crystals

Abstract

We have studied the in- and out-of-plane magnetic penetration depths in the hole-doped iron-based superconductor Ba1−xKxFe2As2 (Tc≈30 K). Single crystals grown from different fluxes and by different groups showed nearly identical results. The in-plane London penetration depth λab is not exponentially saturating at low temperature, as would be expected from a fully gapped superconductor. Instead, λab(T) shows a power-law behavior, λ∝Tn (n≈2), down to T≈0.02Tc, similar to the electron-doped Ba(Fe1−xCox)2As2. The penetration depth anisotropy γλ=λc(T)/λab(T) increases upon cooling, opposite to the trend observed in the anisotropy of the upper critical field, γξ=Hc2⊥c(0)/Hc2∥c(0). These are universal characteristics of both the electron- and hole-doped 122 systems, suggesting unconventional multigap superconductivity. The behavior of the in-plane superfluid density ρab(T) is discussed in light of existing theoretical models proposed for the iron pnictide superconductors.

Source-reported materials — not catalogue approval

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