Josephson effect in a multi-orbital model for Sr$_{2}$RuO$_{4}$

Abstract

We study Josephson current between s-wave/spin-triplet superconductor junctions by taking into account details of band structures in Sr$_{2}$RuO$_{4}$ such as three conduction bands, spin-orbit interaction in the bulk and that at the interface. We assume five superconducting order parameters in Sr$_{2}$RuO$_{4}$: a chiral p-wave symmetry and four helical p-wave symmetries. We calculate current-phase relationship $I(\varphi)$ in these junctions, where $\varphi$ is the macroscopic phase difference between two superconductors. The results for a chiral p-wave pairing symmetry show that $\cos(\varphi)$ term appears in the current-phase relation due to time-reversal symmetry (TRS) breaking. On the other hand, $\cos(\varphi)$ term is absent in the helical pairing states which preserve the TRS. We also study the dependence of maximum Josephson current $I_c$ on an external magnetic flux $\Phi$ in a corner junction. The calculated results of $I_c(\Phi)$ show a relation $I_{c}(\Phi) \neq I_{c}(-\Phi)$ in a chiral state and $I_{c}(\Phi)=I_{c}(-\Phi)$ in a helical state. We calculate $I_c(\Phi)$ in a corner and a symmetric SQUIDs geometry. In a symmetric SQUID geometry, the relation $I_{c}(\Phi)=I_{c}(-\Phi)$ is satisfied for all the pairing states and it is impossible to distinguish chiral state from helical one. On the other hand, results for a corner SQUID always show $I_{c}(\Phi) \neq I_{c}(-\Phi)$ and $I_{c}(\Phi)=I_{c}(-\Phi)$ for a chiral and a helical states, respectively. Experimental tests of these relations in a corner junctions and SQUIDs may serve as a tool for unambiguous determination of the pairing symmetry in Sr$_{2}$RuO$_{4}$.