Condensed Matter Seminar – Niels Bohr Institute - University of Copenhagen

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Condensed Matter Seminar

Search for Time-Reversal-Symmetry-Breaking Effects in Unconventional Superconductors

BCS theory of conventional superconductivity is based on pairing of each electron state with its exact time reverse, resulting in a coherent condensate of spin singlet pairs, which is insensitive to non-magnetic scattering (Anderson theorem). Such superconductors are characterized by a simple order parameter (which breaks U(1)-gauge symmetry) leading to the basic properties, such as the Meissner effect, persistent current and flux quantization. By contrast, unconventional superconductors exhibit additional broken symmetries, which lead often to distinctive superconducting phases with unique properties. Of particular interest is time reversal symmetry breaking (TRSB) which involves magnetism and is predicted to exhibit interesting anomalous properties. However, testing for TRSB is usually difficult due to the weakness of the effect. In this talk we will review our recent studies of TRSB in several superconducting systems, using a unique instrument that was invented for these studies and allow for measuring unprecedentedly minute non-reciprocal optical rotations.

Speaker: Aharon Kapitulnik, Stanford University