Hybridization and correlation effects in the photoemission spectra of RNi2 (R=Ce, Pr, and Nd).

Abstract

Electronic structures of R${\mathrm{Ni}}_{2}$ (R=Y, Ce, Pr, and Nd) are investigated systematically by using photoemission spectroscopy (PES) and compared with those of R${\mathrm{Co}}_{2}$. Double-peak structures are observed in the R 4f PES spectra, in which the spectra weight near ${\mathit{E}}_{\mathit{F}}$ decreases from Ce to Pr and Nd, suggesting a decrease in the R 4f--Ni 3d hybridization from Ce to Pr and Nd. For the same R, the spectral weight near ${\mathit{E}}_{\mathit{F}}$ in R${\mathrm{Ni}}_{2}$ is smaller than that in R${\mathrm{Co}}_{2}$, implying a smaller R 4f hybridization with Ni 3d electrons in R${\mathrm{Ni}}_{2}$ than with Co 3d electrons in R${\mathrm{Co}}_{2}$. These trends are consistent with those in the calculated hybridization matrix elements for ${\mathit{RM}}_{2}$ (M=Co and Ni). A pronounced Ni 3d satellite is observed, which arises from Ni 3d Coulomb correlation effects. The Ni 3d partial spectral weight distribution in R${\mathrm{Ni}}_{2}$ exhibits important discrepancies from the calculated Ni 3d angular momentum projected local density of states (PLDOS), such as peak positions and line shapes, indicating substantial Ni 3d correlation effects. These discrepancies are qualitatively similar to, and quantitatively larger than, those for R${\mathrm{Co}}_{2}$. Quasiparticle spectral densities are calculated by using the Hubbard Hamiltonian and including Co and Ni 3d electron correlation effects, which yield a better agreement with PES spectra than the local-density approximation PLDOS's.