Relativistic Mott transitions, quantum criticality, and finite-temperature effects in tunable Dirac materials from functional renormalization

Abstract: Gross-Neveu-Yukawa-type models such as the chiral Ising, chiral XY, and chiral Heisenberg models, serve as effective descriptions of two-dimensional Dirac semi-metals undergoing quantum phase transitions into various symmetry-broken ordered states. Their relativistic quantum critical points govern the systems' physical behavior in the vicinity of the transition also at finite temperatures, which is strongly influenced by critical order-parameter and chiral fermion fluctuations. Here, we explore the effect of these fluctuations at zero and finite temperature, both in the Dirac phase and in the Mott phases with spontaneously broken symmetry. To that end, we set up a functional renormalization group approach, which allows us to systematically calculate the quantum phase diagrams and scaling behavior at and near quantum criticality. We explicitly estimate quantum critical exponents, calculate the quasiparticle weight of the chiral Dirac excitations, and determine the extent of the quantum critical fan. Furthermore, we expose a semi-metallic precondensation regime where order-parameter fluctuations destroy order at finite temperature and we show the related manifestation of the Coleman-Hohenberg-Mermin-Wagner theorem. For the chiral XY model, we also expose signatures of Berezinskii-Kosterlitz-Thouless physics in a system that includes strong fermion fluctuations. In view of recent experimental developments on correlated phases in highly tunable two-dimensional Dirac materials, our work aims at a more comprehensive theoretical description of relativistic quantum criticality in semi-metals, including non-Dirac-liquid behavior.