Leggett modes and multi-band superconductivity in Sr2RuO4

Abstract

Sr${}_2$RuO${}_4$ is a prototypical multi-band superconductor with three bands crossing the Fermi level. These bands exhibit distinct dimensional characteristics, with one quasi-2D $\gamma$-band and two quasi-1D $\alpha$- and $\beta$-bands. This leads to the expectation that the superconductivity on the $\gamma$-band may be only weakly Josephson-coupled to that on the other two bands. Based on an explicit microscopic weak coupling calculation appropriate for Sr${}_2$RuO${}_4$, we study the collective Leggett modes associated with the relative phase oscillations between the bands and show that a relatively soft Leggett mode exists due to the comparatively weaker inter-band Josephson coupling. These calculations also provide insight into why the superconducting gap magnitudes may be comparable on all three bands, despite the noticeable differences between the $\gamma$ and $\alpha ,\beta$ bands. The analyses can be readily applied to other multi-band superconductors.

Published version, 9 pages, 2 figures

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• Simultaneous Evidence for Pauli Paramagnetic Effects and Multiband Superconductivity in KFe${}_2$As${}_2$ by Small-Angle Neutron Scattering Studies of the Vortex Lattice
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• Skyrmions formation due to unconventional magnetic modes in anisotropic multi-band superconductors
• Interband interference effects at the edge of a multiband chiral p-wave superconductor
• Identifying the dominant pairing interaction in high-$T_c$ FeSe superconductors through Leggett modes
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• Pairing around a Single Dirac Point: A Unifying View of Kohn-Luttinger Superconductivity in Chern Bands, Quarter Metals, and Topological Surface States