Spontaneous symmetry breaking and electronic and dielectric properties in commensurate La7/4Sr1/4CuO4 and La5/3Sr1/3NiO4

Abstract

Complex ordered phases involving spin and charge degrees of freedom in condensed matter, such as layered cuprates and nickelates, are exciting but not well understood solid-state phenomena. The rich underlying physics of the overdoped high-temperature superconductor $\mathrm{L}{\mathrm{a}}_{7/4}\mathrm{S}{\mathrm{r}}_{1/4}\mathrm{Cu}{\mathrm{O}}_{4}$ and colossal dielectric constant insulator $\mathrm{L}{\mathrm{a}}_{5/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Ni}{\mathrm{O}}_{4}$ is studied from first principles within density functional (perturbation) theory, including an effective Hubbard potential $U$ for the exchange and correlation of $d$ orbitals. Charge density wave (CDW) and spin density wave (SDW) orders are found in both materials, where the stripes are commensurate with the lattice. The SDWs are accompanied by complex antiferromagnetic spin arrangements along the stripes. The first series of conduction bands related to the pseudogap observed in the cuprate are found to be directly related to CDW order, while the colossal dielectric constant in the nickelate is demonstrated to be a result of vibronic coupling with CDW order. Differences between the two oxides are related to how the stripes fill with carriers.