Metamagnetism and Critical Fluctuations in High Quality Single Crystals of the Bilayer RuthenateSr3Ru2O7

We report the results of low temperature transport, specific heat, and magnetization measurements on high quality single crystals of the bilayer perovskite ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$, which is a close relative of the unconventional superconductor ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$. Metamagnetism is observed, and transport and thermodynamic evidence for associated critical fluctuations is presented. These relatively unusual fluctuations might be pictured as variations in the Fermi surface topography itself.