Anisotropic up to 92 T and the signature of multiband superconductivity in Ca (Pt As )((Fe Pt ) As )

Abstract

The upper critical fields H c2(T) of single crystals of the superconductor Ca 10(Pt 4-δAs 8)((Fe 0.97Pt 0.03) 2As 2) 5 (δ0.246) are determined over a wide range of temperatures down to T=1.42 K and magnetic fields of up to μ 0H92 T. The measurements of anisotropic H c2(T) curves are performed in pulsed magnetic fields using radio-frequency contactless penetration depth measurements for magnetic field applied both parallel and perpendicular to the ab plane. Whereas a clear upward curvature in Hc2(T) along Hc is observed with decreasing temperature, the Hc2ab(T) along Hab shows a flattening at low temperatures. The rapid increase of the Hc2c(T) at low temperatures suggests that the superconductivity can be described by two dominating bands. The anisotropy parameter γ HHc2ab/Hc2c is ∼7 close to T c and decreases considerably to ∼1 with decreasing temperature, showing rather weak anisotropy at low temperatures. © 2012 American Physical Society.