In an externally applied magnetic field, ultra-pure crystals of the bilayer ruthenate compound Sr3Ru2O7 undergo a metamagnetic transition at a temperature which approaches zero as B approaches a critical value. This "metamagnetic quantum critical point", however, is enveloped by a nematic fluid phase with order one resistive anisotropy in the ab plane. In this talk, I will discuss the microscopic origins of metamagnetism and the accompanying nematic order in this system. I propose that both can be understood within the framework of an orbital-ordering tendency of the material and present a phase diagram which accounts for much of the experimentally observed phenomena.
By contrast, the closely related monolayer compound, Sr2RuO4, is a spin-triplet superconductor; it does not exhibit metamagnetism or nematic order. This drastic difference in the physical properties of the two materials - despite their structural similarity - points towards a possible microscopic mechanism of triplet superconductivity in Sr2RuO4. I will conclude the talk with a discussion of our recent progress in understanding the microscopic origins of superconductivity in Sr2RuO4. |
