Optical properties of superconduct

A fundamental optical study was performed on superconducting (Formula presented)(Formula presented)(Formula presented)(Formula presented) by using a high-accuracy universal polarimeter (HAUP). As this crystal is strongly linearly dichroic, we developed the extended HAUP theory which includes the treatments of the optical dichroisms. After having determined the optical nature of the crystal, we applied the extended HAUP method to a thin (001) plate specimen with light traveling to the front and rear directions in the specimen. These two experiments permitted us to separate the reciprocal and nonreciprocal optical effects. No sign of the nonreciprocal effects was found in the HAUP transmission experiment. A gyration tensor component (Formula presented) takes place suddenly at (Formula presented) (90 K), increases with decreasing temperature, and reaches 1.87×(Formula presented) (36°/mm of rotatory power) at 15 K. A steep change of birefringence Δn with temperature also occurs below (Formula presented). From the behaviors of (Formula presented) and Δn with temperature, it can be concluded that the crystal undergoes a second-order phase transition at (Formula presented) into an optically active class. The crystal manifests large linear dichroism, i.e., Δm=-2.2×(Formula presented).