Measurement of the spontaneous polar Kerr effect in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ and ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$

The existence of spontaneous polar Kerr rotation in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ single crystals and ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_7$ thin films was tested using a Sagnac interferometer. Observation of this effect would be strong evidence that the superconductivity in the cuprates is described by a theory that predicts broken time-reversal symmetry. The Kerr effect was analyzed for both a spatially fluctuating component (anticipating domains) and absolute offset. Neither effect was observed within the sensitivity of the apparatus. The drift of the apparatus sets an upper limit for the offset component at 10 μrad. The noise places an upper limit of 3 μrad on the standard deviation of the spatial fluctuation of the effect.