Limits on superconductivity-related magnetization inSr2RuO4andPrOs4

Abstract

We present scanning superconducting quantum interference device microscopy data on the superconductors Sr 2 RuO 4 ͑T c = 1.5 K͒ and PrOs 4 Sb 12 ͑T c = 1.8 K͒. In both of these materials, superconductivity-related timereversal 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 p x Ϯ ip y 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 ϳ0.1% and ϳ0.2% of the expected magnitude, respectively. Alternatively, if the magnetization is of the expected order, the typical domain size is limited to ϳ30 nm for random domains or ϳ500 nm for periodic domains.

Suppression of spontaneous currents inSr2RuO4by surface disorder

“…The energetic cost of the domain boundaries would be small, due to the very weak dispersion of the electronic band structure along the c direction, and symmetry requires that no spontaneous current would flow at these boundaries. The measurements of Hicks et al 10 place an upper bound of 20 − 400nm on the height of such domains, depending on microscopic domain details, and again assuming Matsumoto-Sigrist predictions for edge currents 12 (similar bounds have not been estimated for the experimental geometries of refs. 5 and 11).…”

“…Though this is the leading phenomenological hypothesis, it is seemingly contradicted by several experiments. Prominent among these are high resolution scanning magnetometry measurements [9][10][11] , which image magnetic fields across several µm of sample (including the sample edge) and see no sign of the expected spontaneous currents.…”

Stability of topological defects in chiral superconductors: London theory

“…Alternatively, for a fixed chirality eqn. (12) demonstrates the absence of the field-reversal splitting of H c1,v . It should be noted however that inclusion of the vortex core energy in (10) which tend to be chirality-dependent 26 will result in non-zero field-reversal splitting of H c1,v .…”

“…3,4 for review) which is corroborated by µSR 5,6 , Kerr effect 7 and phase-sensitive measurements 8,9 . The candidacy of Sr 2 RuO 4 is however undermined by the fact that several attempts to detect surface magnetic field generated by the chiral currents [10][11][12][13] or the magnetic moment associated with them 14 have not yielded a positive result. One of the possible explanations aimed to cut this Gordian knot of seemingly contradicting observations is to assume the presence, on a mesoscopic scale, of an alternating chiral domain structure which leads to the substantial field cancellation.…”

“…Refs. 15,16) or on finding the distribution of magnetic fields assuming a particular domain structure without attempts to justify the latter [10][11][12]17,18 . In this work we use London theory to address the question of the thermodynamic stability of several domain configurations for a simple sample's geometry (such as cylindrical) where demagnetizing effects can be easily taken into account.…”