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arXiv · 2101.06972

Superconducting state of Sr$_2$RuO$_4$ in the presence of longer-range Coulomb interactions

Astrid T. Rømer·P. J. Hirschfeld·Brian M. Andersen
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Abstract

The symmetry of the superconducting condensate in Sr$_2$RuO$_4$ remains controversial after nuclear magnetic resonance (NMR) experiments recently overturned the dominant chiral $p$-wave paradigm. Several theoretical proposals have been put forward to account for existing experiments, including a $d+ig$-wave admixture, conjectured to be stabilized by longer-range Coulomb interactions. We perform a material-specific microscopic theoretical study of pairing by spin- and charge-fluctuations in Sr$_2$RuO$_4$, including the effects of spin-orbit coupling, and both local and longer-range Coulomb repulsion. The latter has important consequences for Sr$_2$RuO$_4$ due to the near-degeneracy of symmetry-distinct pairing states in this material. We find that both the $g$- and $d_{x^2-y^2}$-wave channels remain noncompetitive compared to leading nodal $s'$, $d_{xy}$, and helical ($p$) solutions. This suggests nodal time-reversal symmetry broken $s'+id_{xy}$ or $s'+ip$ phases, promoted by longer-range Coulomb repulsion, as the most favorable candidates for Sr$_2$RuO$_4$. We analyse the properties of these states, and show that the $s'+id_{xy}$ solution agrees with the bulk of available experimental data, including recent discoveries from NMR, muon spin relaxation ($\mu$SR), and ultrasound measurements.

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Astrid T. Rømer, P. J. Hirschfeld, Brian M. Andersen. 2021-01-18. Superconducting state of Sr$_2$RuO$_4$ in the presence of longer-range Coulomb interactions. https://doi.org/10.1103/physrevb.104.064507

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