Anomalous Josephson network in the Ru-Sr²RuO⁴ eutectic system

We measured the c-axis current-voltage (I-V) characteristics of Sr ²RuO⁴ and Ru-enriched Sr²RuO⁴ eutectic systems. Our results revealed that the 3-K phase in the Ru-Sr ²RuO⁴ eutectic system forms a complex Josephson network, which dominates the critical current of the system even at temperatures below bulk T^c. We also found that this Josephson network exhibits anomalous asymmetric features in I-V characteristics, such that the critical current density at positive current J^c₊ differs from that at negative current J^c_- by 5% at 0.3 K. This unusual behavior diminishes with increasing temperature or magnetic field. It disappears at temperatures above 2.3 K at zero field, or above 0.2 T at 0.3 K. We discuss these unusual behaviors in terms of a recent theory that argues a time reversal symmetry breaking transition in the 3-K phase.