Superconducting gaps for Sr₂RuO₄ and their manifestations on observables

The superconducting gap of the Sr2RuO4 is still unknown [1]. The most recent striking inconsistency is observed under uniaxial pressure. While high-sensitivity specific heat measurements detect only one transition temperature [2], muon spin relaxation experiments suggest two [3]. Because the minimal effective model of Sr2RuO4 involves multiple orbitals coupled by spin-orbit interaction, the possible gap functions are extremely intricate and possess odd-frequency contributions [4]. Starting from a model Hamiltonian, we compute the specific heat, the spectral weight and the band diagram expected for various superconducting order parameters. We inspect the effect of inter-orbital pairing on those quantities and we generalize the formalism to account for frequency dependent gap functions.

[1] Mackenzie et al., npj Quantum Materials 2, 40 (2017)  

[2] Li et al., PNAS March 9, 2021 118 e2020492118 (2020)

[3] Grinenko et al., Nature Physics 17, pages 748–754 (2021)

[4] Gingras et al., Phys. Rev. Lett. 123, 217005 (2019), Gingras et al., in preparation.