Universality in antiferromagnetic strange metals

TL;DR

This paper develops a comprehensive theory for metals at the spin-density wave quantum critical point in 2D, providing critical exponents and universal power-laws relevant for heavy-fermion and iron pnictide experiments.

Contribution

It introduces a novel renormalization group approach in frequency space to analyze full Fermi surfaces and Landau damping in quantum-critical metals.

Findings

Critical exponents for thermodynamics and response functions are estimated.

Flow equations are solved analytically and numerically for electron-spin wave interactions.

The method captures Fermi surface changes and Landau damping during the RG flow.

Abstract

We propose a theory of metals at the spin-density wave quantum critical point in spatial dimension $d=2$. We provide a first estimate of the full set of critical exponents (dynamical exponent $z=2.13$, correlation length $\nu =1.02$, spin susceptibility $\gamma = 0.96$, electronic non-Fermi liquid $\eta^f_\tau = 0.53$, spin-wave Landau damping $\eta^b_\tau = 1.06$), which determine the universal power-laws in thermodynamics and response functions in the quantum-critical regime relevant for experiments in heavy-fermion systems and iron pnictides. We present approximate numerical and analytical solutions of Polchinski-Wetterich type flow equations with soft frequency regulators for an effective action of electrons coupled to spin-wave bosons. Performing the renormalization group in frequency -instead of momentum- space allows to track changes of the Fermi surface shape and to capture Landau damping during the flow. The technique is easily generalizable from models retaining only patches of the Fermi surface to full, compact Fermi surfaces.