Effects of deep superconducting gap minima and disorder on residual thermal transport in Sr2RuO4

Recent thermal conductivity measurements on ${\mathrm{Sr}}₂{\mathrm{RuO}}₄$ [E. Hassinger et al., Phys. Rev. X 7, 011032 (2017)] were interpreted as favoring a pairing gap function with vertical line nodes while conflicting with chiral $p$-wave pairing. Motivated by this work we study the effects of deep superconducting gap minima on impurity induced quasiparticle thermal transport in chiral $p$-wave models of ${\mathrm{Sr}}₂{\mathrm{RuO}}₄$. Combining a self-consistent $T$-matrix analysis and self-consistent Bogoliubov--de Gennes calculations, we show that the dependence of the residual thermal conductivity on the normal state impurity scattering rate can be quite similar to the $d$-wave pairing state that was shown to fit the thermal conductivity measurements, provided the normal state impurity scattering rate is large compared with the deep gap minima. Consequently, thermal conductivity measurements on ${\mathrm{Sr}}₂{\mathrm{RuO}}₄$ can be reconciled with a chiral $p$-wave pairing state with deep gap minima. However, the data impose serious constraints on such models and these constraints are examined in the context of several different chiral $p$-wave models.