Resistivity in the vicinity of a van Hove singularity: Sr₂RuO₄ under uniaxial pressure

We report the results of a combined study of the normal-state resistivity and superconducting transition temperature T_c of the unconventional superconductor Sr₂RuO₄ under uniaxial pressure. There is strong evidence that, as well as driving T_c through a maximum at similar to 3.5 K, compressive strains epsilon of nearly 1% along the crystallographic [100] axis drive the gamma Fermi surface sheet through a van Hove singularity, changing the temperature dependence of the resistivity from T² above, and below the transition region to T^1.5 within it. This occurs in extremely pure single-crystals in which the impurity contribution to the resistivity is <100 nΩ cm, so our study also highlights the potential of uniaxial pressure as a more general probe of this class of physics in clean systems.