Invitation Only
Talk 1:
Magnetic quantum criticality: The role of the Fermi surface geometry
Alessandro Toschi, TU Wien
In this talk, I will present our new results on magnetic quantum phase transitions in bulk correlated metals. Specifically, we focus on the 3D Hubbard model on various cubic lattices as a function of temperature and electronic density to determine the relevant regimes around its quantum magnetic transition—namely, the classical, quantum critical, and quantum disordered regimes—as well as the corresponding thermal and non-thermal quantum critical exponents. Our numerical results, obtained via dynamical mean-field theory and supported by analytical derivations, rigorously demonstrate how and why the presence of different types of Kohn anomalies on the underlying Fermi surface: (i) drives the quantum critical behavior above the quantum critical point, (ii) shapes the surrounding phase diagram, and (iii) modifies the Fisher relation linking the thermal quantum critical exponents. Our findings highlight the necessity of explicitly including such geometric properties of the Fermi surface when defining the universality class for magnetic quantum phase transitions in correlated metals.
Talk 2:
Quantum criticality in the two-dimensional Hubbard model
Jan von Delft, Ludwig-Maximilians-Universität München
We study the normal-state, doping-driven phase diagram of the square-lattice Hubbard model using four-patch DCA+NRG. In a parameter regime relevant for cuprates, U = 7t and t′ = −0.3t, we find a critical doping p∗ that marks a continuous quantum phase transition between a pseudogap metal at at p > p∗ and a normal Fermi liquid at p < p∗. In the pseudogap regime, the coherent low-energy spectral weight in the antinodal region is lost and replaced by a narrow, metallic pseudogap, while the nodal region evolves smoothly and remains comparatively coherent, giving rise to Fermi arcs. Close to p∗, we find x = ω/T scaling for various dynamical susceptibilities, and the cluster contribution to the optical conductivity obeys Tσ′(ω, T) ∼ tanh(x/2)/x, implying a 1/T cluster dc-conductivity. In the scaling regime, the vertex contribution to the cluster optical response is much larger than the bubble contribution. We further find evidence for a marginal-Fermi-liquid nodal self-energy.