Observation of broken time-reversal symmetry in the heavy-fermion superconductor UPt 3

• Published in: Science (American Association for the Advancement of Science) Vol. 345; no. 6193; pp. 190 - 193
• Main Authors: Schemm, E. R., Gannon, W. J., Wishne, C. M., Halperin, W. P., Kapitulnik, A.
• Format: Journal Article
• Language: English
• Published: 11.07.2014
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1248552

Optically probed superconductor The exotic superconductor UPt 3 has two superconducting phases that appear at different temperatures, but their nature remains unclear. Schemm et al. shone circularly polarized light on a crystal of UPt 3 and studied its reflection (see the Perspective by van der Marel and Sawatzky). In the low-temperature phase, the pairs of electrons that make the material superconducting have a handedness to them. The finding narrows down the possible descriptions of the electron-pair wave function. Science , this issue p. 190 ; see also p. 138 Optical measurements elucidate the nature of superconductivity in an exotic compound. [Also see Perspective by van der Marel and Sawatzky ] Models of superconductivity in unconventional materials can be experimentally differentiated by the predictions they make for the symmetries of the superconducting order parameter. In the case of the heavy-fermion superconductor UPt 3 , a key question is whether its multiple superconducting phases preserve or break time-reversal symmetry (TRS). We tested for asymmetry in the phase shift between left and right circularly polarized light reflected from a single crystal of UPt 3 at normal incidence and found that this so-called polar Kerr effect appears only below the lower of the two zero-field superconducting transition temperatures. Our results provide evidence for broken TRS in the low-temperature superconducting phase of UPt 3 , implying a complex two-component order parameter for superconductivity in this system.