Metal-Insulator and Magnetic Phase Diagram of Ca2RuO4 from Auxiliary Field Quantum Monte Carlo and Dynamical Mean Field Theory

Layered perovskite ruthenium oxides exhibit a striking series of metal-insulator and magnetic-nonmagnetic phase transitions easily tuned by temperature, pressure, epitaxy, and nonlinear drive. In this work, we combine results from two complementary states of the art many-body methods, Auxiliary Field Quantum Monte Carlo and Dynamical Mean Field Theory, to determine the low-temperature phase diagram of Ca2RuO4. Both methods predict a low-temperature pressure-driven metal-insulator transition coincident with a structural transition and accompanied by a ferromagnetic-antiferromagnetic transition. The properties of the ferromagnetic state are dominated by the ruthenium xy orbital while properties of the antiferromagnetic state are dominated by the xz and yz orbitals. Differences of detail in the predictions of the two methods are analyzed. The work is theoretically important as an application of the auxiliary field quantum Monte Carlo method to an orbitally degenerate system with both Mott and Hunds physics and provides an important comparison of the dynamical mean-field and auxiliary field quantum Monte Carlo methods.