Limits on Superconductivity-Related Magnetization in Sr$_2$RuO$_4$ and PrOs$_4$Sb$_{12}$ from Scanning SQUID Microscopy

TL;DR

This study uses scanning SQUID microscopy to investigate superconductivity-related magnetization in Sr$_2$RuO$_4$ and PrOs$_4$Sb$_{12}$, finding no spontaneous magnetization and constraining possible domain sizes and magnetic field magnitudes.

Contribution

First direct visualization attempt of superconductivity-related magnetic fields in Sr$_2$RuO$_4$ and PrOs$_4$Sb$_{12}$, setting limits on domain sizes and magnetic induction.

Findings

No spontaneous magnetization observed in either material.

Limits on domain wall and edge magnetic fields to less than ~0.1-0.2% of expected.

Domain size constraints of ~30 nm (random) or ~500 nm (periodic) if magnetization exists.

Abstract

We present scanning SQUID microscopy data on the superconductors Sr2RuO4 (Tc = 1.5 K) and PrOs$_4$Sb$_{12}$ (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 Sr$_2$RuO$_4$ nor PrOs$_4$Sb$_{12}$ do we observe spontaneous superconductivity-related magnetization. In Sr$_2$RuO$_4$, many experimental results have been interpreted on the basis of a $px \pm ipy$ 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.