Superconducting state of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Sr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>RuO</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> in the presence of longer-range Coulomb interactions
Astrid T. Rømer, P. J. Hirschfeld, Brian M. Andersen
Abstract
The material Sr${}_{2}$RuO${}_{4}$ is notorious for the difficulty in reconciling all experimental characterizations of its superconducting order parameter. In this theoretical study, the authors explore what superconducting order parameters are most favorable from the perspective of spin-fluctuation mediated pairing, taking into account the multiorbital nature of the system and its sizable spin-orbit coupling. They find that longer-range Coulomb interactions induce a near-degeneracy between nodal $s$-wave and ${d}_{x\phantom{\rule{0}{0ex}}y}$ superconductivity, suggesting a ground-state condensate with time-reversal symmetry breaking of the form $s+i\phantom{\rule{0}{0ex}}{d}_{x\phantom{\rule{0}{0ex}}y}$.