Ca$_{3}$Ru$_{2}$O$_{7}$: Interplay among degrees of freedom and the role of the exchange-correlation

Abstract

Ca$_{3}$Ru$_{2}$O$_{7}$ is a fascinating material that displays physical properties governed by spin-orbit interactions and structural distortions, showing a wide range of remarkable electronic phenomena. Here, we present a density-functional-based analysis of the interplay among degrees of freedom, such as magnetism, Coulomb repulsion (Hubbard-U), and structural degrees of freedom, considering two exchange-correlation methods: Local-Density Approximation (LDA) and Perdew-Burke-Ernzerhof revised for solids (PBEsol). Our goal is twofold: first, to provide a brief overview of the current state of the art on this compound underpinning the last proposed theoretical models and experimental research, and second, to give another view to model the electronic properties compared with the previous theoretical models. Our findings show that Ca$_{3}$Ru$_{2}$O$_{7}$ displays several electronic states (metal, semimetal, and narrow insulator) as a function of Hubbard-U while it exhibits structural transition depending on the functional. We disentangle the effect of the different degrees of freedom involved, clarifying the role of exchange-correlation in the observed electronic and structural transitions.