Local Tunneling Spectroscopy across a Metamagnetic Critical Point in the Bilayer RuthenateSr3Ru2O7

Abstract

The local spectroscopic signatures of metamagnetic criticality in ${\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ were explored using scanning tunneling microscopy (STM). Singular features in the tunneling spectrum were found close to the Fermi level, as would be expected in a Stoner picture of itinerant electron metamagnetism. These features showed a pronounced magnetic field dependence across the metamagnetic critical point, which cannot be understood in terms of a naive Stoner theory. In addition, a pseudogap structure was observed over several tens of meV, accompanied by a $c(2\times 2)$ superstructure in STM images. This result represents a new electronic ordering at the surface in the absence of any measurable surface reconstruction.