Effects of Strong Interactions in a Half Metallic Magnet: a Determinant Quantum Monte Carlo Study

Understanding the effects of electron-electron interactions in half metallic magnets (HMs), which have band structures with one gapped spin channel and one metallic channel, poses fundamental theoretical issues as well as having importance for their potential applications. Here we use determinant quantum Monte Carlo to study the impacts of an on-site Hubbard interaction $U$, finite temperature, and an external (Zeeman) magnetic field on a bilayer tight-binding model which is a half-metal in the absence of interactions, by calculating the spectral density, conductivity, spin polarization of carriers, and local magnetic properties. We quantify the effect of $U$ on the degree of thermal depolarization, and follow relative band shifts and monitor when significant gap states appear, each of which can degrade the HM character. For this model, Zeeman coupling induces, at fixed particle number, two successive transitions: compensated half-metal with spin-down band gap $\rightarrow$ metallic ferromagnet $\rightarrow$ saturated ferromagnetic insulator. However, over much of the more relevant parameter regime, the half-metallic properties are rather robust to $U$.