Identification of Spin-Triplet Superconductivity through a Helical-Chiral Phase Transition in Sr$_2$RuO$_4$ Thin-Films

TL;DR

This paper proposes a method to identify spin-triplet superconductivity in Sr$_2$RuO$_4$ thin-films by detecting a unique helical-chiral phase transition induced by magnetic fields, observable via tunneling conductance changes.

Contribution

It introduces a novel approach to detect spin-triplet pairing by observing a phase transition in thin-films using surface state properties and tunneling spectroscopy.

Findings

Spin-triplet superconductors undergo a helical to chiral phase transition under magnetic fields.

This phase transition causes a significant change in surface Andreev bound states.

The transition can be detected through tunneling conductance measurements.

Abstract

Despite much effort for over the two decades, the paring symmetry of a Sr$_2$RuO$_4$ superconductor has been still unclear. In this Rapid Communication, motivated by the recent rapid progress in fabrication techniques for Sr$_2$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 physics of spin-triplet superconductivity.