Deconstructing Sr2RuO4: Insights from a microscopic perspective

The nature of the superconducting order parameter in Sr2RuO4 has been topic of active debate since recent spin-susceptibility measurements revealed that it should be a spin-singlet state [1], contradicting the previous understanding of this material as a chiral p-wave superconductor. Together with the evidence for broken time-reversal symmetry [2,3] and a jump in the shear modulus c66 at the superconducting transition temperature [4,5], experiments point towards an even-parity chiral superconductor with Eg symmetry. This type of order parameter has been consistently been dismissed based on the quasi-two-dimensional electronic structure of this material. In this talk, I discuss how the orbital degree of freedom can encode the two-component nature of the Eg order parameter, allowing for a local orbital-antisymmetric spin-triplet state that can be stabilized by on-site Hund’s coupling [6]. In addition, I will highlight recent strain and pressure experiments and show how this specific order parameter seems to naturally reconcile the surprising behaviour of the evolution of the critical temperature under strain along different directions. In particular, we can semi-quantitatively account for the asymmetric splitting of the critical temperatures for compressive strain along the 100 direction, and the reduction of the critical temperatures for compressive strain along the 001 and 110 directions with a single free parameter [7]. 

[1] A. Pustogow et al., Nature 574, 72 (2019). 

[2] J. Xia et al., Phys. Rev. Lett. 97, 167002 (2006). 

[3] V. Grinenko et al., Nature Physics 17, 748 (2021). 

[4] S. Benhabib et al., Nature Physics 17, 194 (2021). 

[5] S. Ghosh et al., Nature Physics 17, 199 (2021). 

[6] H. G. Suh et al., Phys. Rev. Research 2, 032023 (2020). 

[7] S. Beck et al., Phys. Rev. Research 4, 023060 (2022).