Identification of spin-triplet superconductivity through a helical-chiral phase transition in Sr2RuO4 thin films

Despite much effort over the past two decades, the pairing symmetry of a ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ superconductor is still unclear. Motivated by the recent rapid progress in fabrication techniques for ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ thin films, we propose a promising strategy for identifying the spin-triplet superconductivity in the thin-film geometry by employing an antisymmetric spin-orbit-coupling potential and a Zeeman potential due to an external magnetic field. We demonstrate that a spin-triplet superconducting thin film undergoes a phase transition from a helical state to a chiral state by increasing the applied magnetic field. This phase transition is accompanied by a drastic change in the property of surface Andreev bound states. As a consequence, the helical-chiral phase transition, which is unique to the spin-triplet superconductors, can be detected through a sudden change in a tunneling conductance spectrum of a normal-metal/superconductor junction. Importantly, our proposal is constructed by combining fundamental and rigid concepts regarding the physics of spin-triplet superconductivity.