Crossover in the nature of the metallic phases in the perovskite-type RNiO_3

Abstract

We have measured the photoemission spectra of Nd${}_{1-x}$Sm${}_x$NiO${}_3$, where the metal-insulator transition and the Néel ordering occur at the same temperature for $x\lesssim 0.4$ and the metal-insulator transition temperature ($T_{MI}$) is higher than the Néel temperature for $x\gtrsim 0.4$. For $x\le 0.4$, the spectral intensity at the Fermi level is high in the metallic phase above $T_{MI}$ and gradually decreases with cooling in the insulating phase below $T_{MI}$ while for $x>0.4$ it shows a pseudogap-like behavior above $T_{MI}$ and further diminishes below $T_{MI}$. The results clearly establish that there is a sharp change in the nature of the electronic correlations in the middle ($x\sim 0.4$) of the metallic phase of the $R$NiO${}_3$ system.

4 pages, 4 figure, submitted to Phys. Rev. B

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