Impact of antiferromagnetism on the optical properties of rare-earth nickelates

Abstract

We study the temperature dependence of the optical conductivity of rare-earth nickelate films of varying composition and strain close to the antiferromagnetic ordering temperature, T N. Two prominent peaks at 0.6 and 1.3 eV, which are characteristic of the insulating phase, display a small but significant increase in intensity when the material passes from para-to antiferromagnetic. This observation indicates the presence of a positive feedback between antiferromagnetic (AF) and bond disproportionation (BD) order. By analyzing the temperature dependence near T N , and using a Landau-type free-energy expression for BD and AF order, we infer that BD order is a necessary condition for the AF phase to appear, and that the antiferromagnetism contributes to stabilization of the bond disproportionation. This model also explains why hysteresis is particularly strong when the transition into the insulating state occurs simultaneously with antiferromagnetic order.

Low-energy description of the metal-insulator transition in the rare-earth nickelates

“…Some of these appear to be consistent with very recent experimental findings from optical spectroscopy [55]. More theoretical and experimental work is obviously needed however to put our low-energy description to the test.…”

“…6 and 7). Indeed, such a splitting has been observed in recent optical spectroscopy experiments [55]. We propose that our low-energy theory provides a theoretical interpretation of this experimental discovery, and hope to support this claim by explicit calculations of optical spectra in future work.…”

Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe2O3 under ultra-high pressures

“…3 to that observed in the rare-earth nickelates (RNiO 3 with R=Sm, Eu, Y, or Lu)[58][59][60][61][62]. In fact, the latter exhibit a site-selective Mott transition, characterized by a two-sublattice symmetry breaking, with formation of site-selective local moments with localized Ni3d magnetic moments and Ni-d-O-p singlet nonmagnetic states.…”

Generic Optical Excitations of Correlated Systems: π -tons

“…The experimental validation of π-tons is more challenging. Indeed, the optical conductivity has been studied for a wide range of materials [56][57][58][59][60][61][62][63]. But now that we know that there are π-tons, too, we need to distinguish these π-tons from excitons or in metals from weak localization corrections.…”