mK-STM Studies of the Temperature- and Field-dependence of the Quasiparticle Spectrum of Sr2RuO4

Atomic-resolution scanning tunneling spectroscopy is used to study the spectrum of quasiparticle states in superconducting Sr2RuO4. The measured temperature dependence of the quasiparticle spectrum is consistent with a multi-band superconducting order parameter with one band exhibiting a line of nodes, if a constant density of states offset can be ascribed to a surface effect. In magnetic fields $H<H_{c2}$, a vortex lattice, square and oriented parallel to the <110> direction of the RuO2 lattice, is detected by spectroscopic imaging. Each vortex exhibits one flux quantum and a strong zero-bias conductance peak.