Superconducting Order Parameter Domains in Strontium Ruthenate Probed by Josephson Interferometry

• Main Author: Kidwingira, Francoise
• Other Authors: Van Harlingen, Dale J.
• Format: Text
• Language: unknown
• Published: 2007
• Subjects: Physics; Condensed Matter; IPY
• Online Access: http://hdl.handle.net/2142/80546

101 p. Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. There is evidence for degenerate chiral order parameters of px +/- ipy symmetry in the superconducting ruthenate Sr 2RuO4 which can lead to the presence of chiral order parameter domains in the material. We study bi-metallic Josephson junctions made of Sr2RuO4 and a conventional superconductor. Their critical current modulations in an applied magnetic field carry information about the phase of the order parameter of the ruthenate. In these junctions, we observe multiple phase interference in a single tunneling direction which indicates the presence of order parameter domains. The domain structure creates in some samples a striking qualitative difference between the magnetic field modulations of the critical current of junctions fabricated on orthogonal faces of a Sr 2RuO4 single crystal. Transitions between the chiral states of a domain or motion of domain walls separating them generates telegraph noise in the critical current as a function of either magnetic field or time, and is responsible for hysteresis observed in field sweeps of the critical current. Cooling the junctions in a magnetic field lifts the degeneracy between the two types of domains. The increased probability of one chirality over the other translates into an enhanced critical current for the junctions. The presence of such domains confirms the suspected p-wave spin triplet and complex nature of the superconducting pairing state in Sr2RuO 4, making it the superconducting analog of the A-phase of superfluid 3He.