Evolution of the Fermi surface and quasiparticle renormalization through a van Hove singularity in Sr_2-yLa_yRuO₄

We employ a combination of chemical substitution and angle resolved photoemission spectroscopy to prove that the Fermi level in the gamma band of Sr2-gamma La gamma RuO4 can be made to traverse a van Hove singularity. Remarkably, the large mass renormalization has little dependence on either k or doping. By combining the results from photoemission with thermodynamic measurements on the same batches of crystals, we deduce a parametrization of the full many-body quasiparticle dispersion in Sr2RuO4 which extends from the Fermi level to approximately 20 meV above it.