Speaker
Description
Heavy-fermion systems [1] have triggered a tremendous amount of experimental and theoretical research since the discovery of quantum criticality and pronounced non-Fermi-liquid behavior in these materials more than two decades ago.
The properties of these compounds are largely derived from localized f orbitals hybridized with broad conduction bands, resulting in a lattice of local moments coupled to an electronic bath via the Kondo interaction.
A vast number of these heavy-fermion compounds, examples including YbRh$_{2}$Si$_{2}$ [2], CeCoIn$_{5}$ [3] or CeRhIn$_{5}$ [4], show a so-called Kondo breakdown (KB) quantum critical point (QCP). Hallmarks of such a KB-QCP are a sudden reconstruction of the Fermi-surface when crossing the QCP at zero temperature and strange metallic behavior at finite temperatures close to the QCP, featuring a linear in temperature resistivity, a $\log T$ dependence of the Sommerfeld coefficient and $\omega/T$ scaling of various dynamical susceptibilities.
I present a model study of a KB-QCP in the periodic Anderson model using two-site Cellular Dynamical Mean-field Theory [5,6] using the Numerical Renormalization Group [7] to solve the self-consistent impurity model. We show that the low temperature phases on both sides of the QCP are Fermi-liquids, which differ in their Fermi-surface volumes. Close to the QCP, these Fermi-liquid fixed points are reached via a two-stage screening process, leading to non-Fermi-liquid behavior at intermediate temperatures. Evidence for a linear in temperature resistivity beyond self-energy effects and a $\log T$ dependence of the Sommerfeld coefficient in the non-Fermi-liquid are provided. Special emphasis is put on $\omega/T$ scaling of the optical conductivity, where we find good qualitative agreement with recent results on YbRh$_{2}$Si$_{2}$ [8].
[1] H. v. Löhneysen, A. Rosch, M. Vojta, and P. Wölfle, Rev. Mod. Phys. 79, 1015 (2007).
[2] O. Trovarelli et al., Phys. Rev. Lett. 85, 626 (2000).
[3] L. Jiao, Y. Chen et al., Proc. Natl. Acad. Sci. 112, 673 (2015).
[4] N. Maksimovic, et al., arXiv:2011.12951 (2020).
[5] L. De Leo, M. Civelli, and G. Kotliar, Phys. Rev. Lett. 101, 256404 (2008).
[6] L. De Leo, M. Civelli, and G. Kotliar, Phys. Rev. B 77, 075107 (2008).
[7] R. Bulla, T. A. Costi, and T. Pruschke, Rev. Mod. Phys. 80, 395 (2008).
[8] L. Prochaska, et al., Science 367, 285 (2020).
