title: Superconductivity. Observation of broken time-reversal symmetry in the heavy-fermion superconductor UPt₃.
abstract: 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 UPt3, 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 UPt3 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 UPt3, implying a complex two-component order parameter for superconductivity in this system.
authors.affiliation: Department of Physics, Stanford University, Stanford, CA 94305, USA. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA. Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA. eschemm@stanford.edu.
authors.forename: E R
authors.initials: ER
authors.lastname: Schemm
authors.affiliation: Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Gannon
authors.affiliation: Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Wishne
authors.affiliation: Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA.
authors.forename: W P
authors.initials: WP
authors.lastname: Halperin
authors.affiliation: Department of Physics, Stanford University, Stanford, CA 94305, USA. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA. Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA. Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.
authors.forename: A
authors.initials: A
authors.lastname: Kapitulnik