Time-reversal symmetry breaking in superconductors: A proposed experimental test

We propose an experiment to test for broken time-reversal symmetry in the high-temperature superconductors. We configure a superconducting quantum interference device (SQUID) in a manner similar to that used recently to test for ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$ symmetry, but where one junction is on a crystal face of arbitrary angle. Assuming a ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$+iε${\mathit{d}}_{\mathit{x}\mathit{y}}$ symmetry, we calculate the magnetic diffraction patterns for the SQUID for various values of ε and angle. For any nonzero ε, i.e., time-reversal symmetry breaking, we find a nonzero circulating current spontaneously arises in the SQUID even in zero applied magnetic field and zero bias current.