A controlled theory of strange metals with a critical Fermi surface

Abstract

I will present a new large N scheme that can describe strongly coupled quantum critical points (QCP) in itinerant Fermion systems. The new scheme captures the two way feedback between fermions and critical bosons self consistently within the large N saddle point rather than in uncontrolled 1/N corrections as in previous schemes. As an application of this approach, I will present a theory of quantum critical points in heavy fermion systems, involving a change in Fermi surface volume without symmetry breaking. Under certain conditions, which I will describe, the theory leads to a marginal Fermi liquid, or ``strange metal", with resistivity linear in the temperature. In the parameter regime of strong damping of emergent bosonic excitations, the QCP also displays a near-universal ``Planckian" transport lifetime, . In the opposite regime of weak boson damping, the QCP realizes a "skewed marginal Fermi liquid" characterized by particle hole asymmetry in the electron spectral function and a sub-Planckian relaxation rate.