Heavy-fermion quantum criticality via two-stage screening

We address a Kondo breakdown quantum critical point (QCP) in heavy-fermion systems by studying the periodic Anderson model using a two-site cellular dynamical mean-field theory (DMFT) approach. By employing the numerical renormalization group (NRG) to solve the effective impurity model, we are able to dispose of the limitations faced by previous two-site DMFT studies. At zero temperature, we find a Kondo breakdown QCP separating two Fermi-liquid (FL) phases, which differ in their Fermi surface volumes. These FL phases are reached via a two-stage screening process, leading to non-Fermi liquid (NFL) behavior at finite temperatures. In this talk, we will specifically focus on frequency over temperature scaling of the optical conductivity in the NFL region, where we find good qualitative agreement with recent experimental results on YbRh₂Si₂.