Van Hove singularity and stress-induced Fermi surface tuning in Sr₂RuO₄

Application of in-plane uniaxial stress to the quasi-2D correlated material Sr₂RuO₄ results in pronounced changes to the physical properties; most familiar is a factor 2.5 increase in superconducting transition temperature. The normal state of Sr₂RuO₄ is also impacted. Specifically, the crossover temperature to standard Fermi Liquid properties can be tuned from T=30 K to almost 0 K with -0.44% strain. These anomalous properties are associated with the proximity of the Fermi energy (E_F) to a sharp singularity in the density of states, which can be tuned to E_F and thus varies strongly on the scale of the Zeeman interaction and thermal energies. Reported here are ¹⁷O NMR hyperfine shifts over a wide range of stress, field, and temperature. Simple modeling of the results indicates that the difference between E_F and the energy of the van Hove singularity plays a dominant role in the normal state properties for temperatures of order 300 K and below.