Strange metallicity in an antiferromagnetic quantum critical model: A sign-problem-free quantum Monte Carlo study

We compute transport and thermodynamic properties of a two-band spin-fermion model describing itinerant fermions in two dimensions interacting via Z2 antiferromagnetic quantum critical fluctuations by means of a sign-problem-free quantum Monte Carlo approach. We show that the phase diagram of this model indeed contains a d-wave superconducting phase at low enough temperatures. However, a crucial question that arises is whether a non-Fermi-liquid metallic regime exists above Tc, exhibiting hallmark strange-metal transport phenomenology. Interestingly, we find that this version of the model describes a non-Fermi-liquid metallic regime that displays an approximately T-linear resistivity above Tc for a strong fermion-boson interaction. Using the Nernst-Einstein relation, our QMC results also show that this strange metal phase exhibits a crossover from being characterized by a charge compressibility given approximately by chi c similar to 1/T at high temperatures to being described by a charge diffusivity consistent with the scaling Dc similar to 1/T at low temperatures. Therefore, our paper adds support to the view that the Z2 antiferromagnetic spin-fermion model at strong coupling can be considered a minimal model that describes both unconventional superconductivity and strange metallicity, which are fundamentally interconnected in many important strongly correlated quantum materials.

Automated summary

We compute the transport and thermodynamic properties of a two-dimensional free fermion model using a quantum Monte Carlo approach. Our results show that the model exhibits a d-wave superconducting phase at low enough temperatures. Additionally, we find that the model also describes a non-Fermi-liquid metallic regime above the superconducting transition temperature, with an approximately linear resistivity for strong fermion-boson interaction.