Normal State, Superconductivity and Quasiparticle Fermi Surface of the Strongly Correlated Oxide Sr₂RuO₄

The oxide superconductor Sr2RuO4 is emerging as an archetypal strongly correlated electron system. We review the experimental situation, focusing on Fermi surface specific probes. Quantum oscillation measurements have revealed a Fermi surface consisting of three slightly warped cylinders populated by quasiparticles with masses ranging from 3.4 to 14.6 times the bare electron mass. Then is strong evidence that Sr2RuO4 is a spin-triplet superconductor, and the simplicity of the Fermi surface combined with detailed knowlege of the quasiparticle properties from quantum oscillation and orbital specific NMR measurements means that Sr2RuO4 may be a key system for understanding unconventional superconductivity. We compare Sr2RuO4 With three-dimensional nearly ferromagnetic 3d-metals, and suggest that quasi-tno-dimensional spin-fluctuations may be responsible for the fact that Sr2RuO4 is the first nearly ferromagnetic metal to show superconductivity. (C) 1999 Elsevier Science B.V. All rights reserved.