Quasiparticles beyond the Fermi liquid and heavy fermion criticality

TL;DR

This paper develops a self-consistent theory for quasiparticles near an antiferromagnetic quantum critical point, explaining non-Fermi liquid behavior and matching experimental data on YbRh2Si2.

Contribution

It introduces a critical quasiparticle theory that accounts for scale-dependent effective mass enhancement in disordered 3D AFM quantum critical systems.

Findings

Derived temperature dependencies of specific heat and resistivity matching experiments.

Identified the role of quasi-2D Gaussian fluctuations in driving 3D critical behavior.

Established a strong coupling solution for the effective mass enhancement equation.

Abstract

We give a self-consistent theory of the scale dependent effective mass enhancement m*/m of quasiparticles by 3D antiferromagnetic (AFM) spin fluctuations in the presence of disorder at an AFM quantum critical point. The coupling of fermionic and bosonic degrees of freedom in the critical regime is described in terms of a critical quasiparticle theory. Using the fact that even in the "non-Fermi liquid" regime the quasiparticle width does not exceed the quasiparticle energy, we adopt relations from Fermi liquid theory to determine the dependence of the spin fluctuation spectrum on m*/m, from which the self energy and hence m*/m may be calculated. The self-consistent equation for m*/m has a strong coupling solution provided the initial value is sufficiently large. We argue that in YbRh2Si2, quasi-2D Gaussian fluctuations existing over a wide range drive the system into the 3D strongly coupled fluctuation regime. We find critical exponents of the temperature dependence of the specific heat coefficient \gamma\propto T^{-1/4} and of the resistivity \rho(T)=\rho(0)+ A T^{3/4} in good agreement with experiments on YbRh2Si2 in the temperature range T < 0.3K.