The Transition Between Real and Complex Superconducting Order Parameter Phases in UPt3

• Published in: Science (American Association for the Advancement of Science) 2010-06, Vol.328 (5984), p.1368-1369
• Main Authors: STRAND, J. D, BAHR, D. J, VAN HARLINGEN, D. J, DAVIS, J. P, GANNON, W. J, HALPERIN, W. P
• Format: Article
• Language: English
• Subjects: Competition; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Critical currents; Electronics; Exact sciences and technology; Fermions; Heavy-fermion superconductors; Order parameters; Phase transitions; Phases; Physics; Properties of type I and type II superconductors; Proximity effects, weak links, tunneling phenomena, and josephson effects, adreev effect, sn and sns junctions; Superconducting materials (excluding high-tc compounds); Superconductivity; Superconductors; Symmetry; Tunnel junctions
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1187943

Order parameter symmetry is one of the basic characteristics of a superconductor. The heavy fermion compound UPt3 provides a rich system for studying the competition between superconductivity and other forms of electronic order and exhibits two distinct superconducting phases that are characterized by different symmetries. We fabricated a series of Josephson tunnel junctions on the as-grown surfaces of UPt3 single crystals spanning the a-b plane. By measuring their critical current, we mapped out the magnitude of the superconducting order parameter as a function of the momentum-space direction and temperature. In the high-temperature phase, we observed a sharp node in the superconducting gap at 45 degrees with respect to the a axis; an out-of-phase component appeared in the low-temperature phase, creating a complex order parameter.