Polar Kerr Effect Measurements of YBa2Cu3O6+x: Evidence for Broken Symmetry Near the Pseudogap Temperature

TL;DR

This study uses high-precision polar Kerr effect measurements to detect broken symmetry in YBa2Cu3O6+x near the pseudogap temperature, indicating a phase transition and time reversal symmetry breaking above room temperature.

Contribution

It provides direct evidence of broken symmetry and a phase transition near the pseudogap temperature in high-Tc superconductor YBCO using advanced Kerr effect measurements.

Findings

Non-zero Kerr rotations appear near pseudogap temperature T*

Evidence of a phase transition at T*

Time reversal symmetry is broken above room temperature

Abstract

Polar Kerr effect in the high-Tc superconductor \YBCO was measured at zero magnetic field with high precision using a cyogenic Sagnac fiber interferometer. We observed non-zero Kerr rotations of order $\sim 1 \mu$rad appearing near the pseudogap temperature $T^*$, and marking what appears to be a true phase transition. Anomalous magnetic behavior in magnetic-field training of the effect suggests that time reversal symmetry is already broken above room temperature.