Evolution of interorbital superconductor to intraorbital spin-density wave in layered ruthenates

Abstract

The ruthenate family of layered perovskites has been a topic of intense interest, with much work dedicated to the superconducting state of Sr_{2}RuO_{4}. Another long-standing puzzle is the lack of superconductivity in its sister compound, Sr_{3}Ru_{2}O_{7}, which constrains the possible mechanisms of Sr_{2}RuO_{4}. Here we address a microscopic mechanism that unifies the orders in these materials. Beginning from a model of Sr_{2}RuO_{4} featuring interorbital spin-triplet pairing via Hund's and spin-orbit couplings, we find that bilayer coupling alone enhances, while staggered rotations destroy interorbital superconductivity. A magnetic field then shifts van Hove singularities, allowing intraorbital spin-density wave order to form in Sr_{3}Ru_{2}O_{7}. Our theory predicts that Sr_{3}Ru_{2}O_{7} without staggered rotations exhibits interorbital superconductivity with a possibly higher transition temperature.