Lower critical fields and the anisotropy in PrFeAsO_(1-y) single crystals

摘要

We report the lower critical fields H_(c1) measurements using a miniature Hall-sensor array on superconducting iron-pnictide PrFeAsO _(1-y) single crystals. The local magnetic induction measured by the sensor at the edge of the crystal clearly resolves the first flux penetration from the Meissner state. The temperature dependence of H_(c1) for H _c is well scaled by the in-plane superfluid density determined by the penetration depth measurements. The anisotropy of H_(c1) at low temperatures is estimated to be ?2.5, which is smaller than the anisotropy of the upper critical fields H_(c2), indicating the multiband superconductivity in this system where the active band for superconductivity is more two-dimensional.