Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 7: SC: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence

TT 7.8: Invited Talk

Monday, March 22, 2010, 16:00–16:30, H20

Polar Kerr Effect of Unconventional Superconductors — •Aharon Kapitulnik — Stanford University, Stanford, CA, USA

BCS theory of conventional superconductivity can be described by a condensate of Cooper-pairs of time-reversed states. Such superconductors respect time reversal symmetry and are insensitive to non-magnetic scattering (the Anderson theorem). For unconventional superconductors, sign-changes in different parts of the Fermi surface results is breakdown of Anderson theorem. In addition, the higher angular momentum state gives rise to the possibility of “chiral" order parameter for which time-reversal symmetry (TRS) is broken. A series of recent studies have shown that ultra-sensitive Polar Kerr effect measurements, using a Sagnac interferometer, can detect such TRS breaking effects in unconventional superconductors [1]. For example, Sr₂RuO₄ has been shown to break TRS, and together with other measurements seem to be consistent with some variant of a “p+ip" type order parameter, while ferromagnet/superconductor bilayer structures show signatures of the “inverse proximity effect" which was long sought after following its first theoretical prediction. In this talk we will review measurements on a variety of systems including the heavy fermion URu2Si2 which has mystified researchers since in this system superconductivity occurs deep inside a mysterious “hidden order" state (whose transition temperature is approximately 17.5 K).

[1] For a recent review of our studies see: Aharon Kapitulnik, Jing Xia, Elizabeth Schemm and Alexander Palevski, New J. Phys. 11 (2009) 055060.