Broken time-reversal symmetry in a SQUID based on chiral superconducting Sr2RuO4

Abstract

Unconventional superconductors involve not only gauge-symmetry breaking but also orbital- and spin-symmetry breaking. Superconducting Sr2RuO4 is known as a spin-triplet chiral p-wave and a topological superconductor with broken time-reversal symmetry (BTRS). Kerr-effect and muon-spin-rotation (pSR) measurements have shown that The bulk superconducting state of Sr2RuO4 features BTRS in The orbital part; hence, it is called The chiral state. BTRS in The response of superconducting junctions or SQUIDs would appear as The shifts of magnetic interference patterns. However, it is problematic to distinguish whether The shift originates in The residual magnetic field (trapped vortex) or The effects of BTRS. Here, we show that The magnetic interference patterns of a SQUID based on Sr2RuO4 are explicitly asymmetric with respect to The direction of both The bias current and The applied magnetic field; namely, there is no inversion symmetry. This indicates that The superconducting state of Sr2RuO4 undoubtedly breaks The time-reversal symmetry of The SQUID.