The odd case of superconductivity in strontium ruthenate

Discovered 24 years ago, strontium ruthenate was rapidly established to be an unconventional superconductor [1]. Further early experiments strongly suggesting a spin-triplet, odd-parity chiral p-wave state – providing a platform for non-Abelian Majorana modes. However, more recent experiments have revealed flaws in this interpretation [2], re-opening key questions: What is the origin of superconductivity? What is the pairing symmetry? These questions are all the more pertinent given that the normal state electronic structure is well understood, so the theory of the superconducting state should be within reach. Fortunately, recent strain experiments provide a new experimental tool that should provide essential insights into this vexing problem [3].

[1] Y. Maeno et al., Nature 372, 532 (1994), A. P. Mackenzie et al., Phys. Rev. Lett. 76, 3786 (1996), M. Rice and M. Sigrist, J. Phys. Cond. Matter 7, L643 (1995).
[2] P. G. Björnsson et al., Phys. Rev. B 72, 012504 (2005), E. Hassinger et al., Phys. Rev. X 7, 011032 (2017).
[3] C. W. Hicks et al., Science 344, 283 (2014), A. Steppke et al., Science 355, 148 (2017).