Spin conservation and a Fermi liquid near a magnetic quantum critical point

A.V. Chubukov, University of Wisconsin-Madison

I propose a new low-energy theory for itinerant fermions near a ferromagnetic quantum critical point. I show that the full low-energy model includes, in addition to conventional interaction via spin fluctuations, another type of interaction, whose presence is crucial for the theory to satisfy SU(2) spin conservation. I demonstrate the consistency between a loop-wise expansion and a Fermi liquid description for the full model. I further show that, prior to the ferromagnetic instability, the system develops a Pomeranchuk-type instability into a state with zero magnetization but with p-wave deformations of the Fermi surfaces of spin-up and -down electrons (a spin nematic).