Speaker: Aharon Kapitulnik, Departments of Applied Physics and Physics,
Stanford University
                                                                                    
Title: Search for Broken Time Reversal Symmetry States in Unconventional
Superconductors
                                                                                    
Abstract:
The Polar Kerr Effect (PKE) is sensitive to time-reversal symmetry
breaking (TRSB) since it measures the existence of an antisymmetric
contribution to the real and?imaginary parts of the frequency-dependent
dielectric tensor, and such a contribution is necessarily absent if TRS is not
broken in the?material.?In order to measure the very small static TRSB effect
in superconductors, we have developed a new PKE technique based on a fiber
Sagnac interferometer with a zero-area Sagnac loop. Initially the technique
has been used to discover TRSB in Sr2RuO4, thus strongly suggesting a p+ip
symmetry for its order parameter. In the talk I will describe the technique
and the detailed studies on Sr2RuO4 as well as subsequent studies of high-Tc
superconductors and selected heavy fermion materials. In particular I will
show PKE results on high quality YBa2Cu3O6+x shedding new light on the origin
of the pseudogap in this system.