Limits on superconductivity-related magnetization in Sr2RuO4 and PrOs4Sb12 from scanning SQUID microscopy

Abstract

We present scanning superconducting quantum interference device microscopy data on the superconductors Sr2RuO4 (Tc=1.5 K) and PrOs4Sb12 (Tc=1.8 K). In both of these materials, superconductivity-related time-reversal symmetry-breaking fields have been observed by muon spin rotation; our aim was to visualize the structure of these fields. However, in neither Sr2RuO4 nor PrOs4Sb12 do we observe spontaneous superconductivity-related magnetization. In Sr2RuO4, many experimental results have been interpreted on the basis of a px±ipy superconducting order parameter. This order parameter is expected to give spontaneous magnetic induction at sample edges and order parameter domain walls. Supposing large domains, our data restrict domain wall and edge fields to no more than ∼0.1% and ∼0.2% of the expected magnitude, respectively. Alternatively, if the magnetization is of the expected order, the typical domain size is limited to ∼30 nm for random domains or ∼500 nm for periodic domains.