Breakdown of the Wiedemann-Franz law at the Lifshitz point of strained Sr2RuO4

Strain tuning Sr2RuO4 through the Lifshitz point, where the Van Hove singularity of the electronic spectrum crosses the Fermi energy, is expected to cause a change in the temperature dependence of the electrical resistivity from its Fermi liquid behavior rho similar to T-2 to rho similar to T(2)log(1/T), a behavior consistent with experiments by Barber et al. [Phys. Rev. Lett. 120. 076602 (2018)]. This expectation originates from the same multiband scattering processes with large momentum transfer that were recently shown to account for the linear in T resistivity of the strange metal Sr3Ru2O7. In contrast, the thermal resistivity rho(Q) T/kappa, where kappa is the thermal conductivity, is governed by qualitatively distinct processes that involve a broad continuum of compressive modes, i.e., long-wavelength density excitations in Van Hove systems. While these compressive modes do not affect the charge current, they couple to thermal transport and yield rho(Q) proportional to T-3/2. As a result, we predict that the Wiedemann-Franz law in strained Sr2RuO4 should be violated with a Lorenz ratio L proportional to T(1/2)log(1/T). We expect this effect to be observable in the temperature and strain regime where the anomalous charge transport was established.