Paramagnon theories below three dimensions

Abstract

We study the magnetic behavior of an itinerant, strongly interacting fermion system for varying values of the coupling constant and for arbitrary dimensionalities $1<d<~3$. We show that, at zero temperature, due to quantum effects, the critical exponents are the mean-field ones below two dimensions as well as above. We then focus on the critical behavior of the two-dimensional case, which, within some assumptions that are discussed, exhibits a ferromagnetic rather than antiferromagnetic character. We also compute the effects of critical fluctuations on the lowtemperature properties of such systems.