Separation of Spin and Charge Densities in La₂NiO_4+δ

Abstract

Separation of spin and charge densities in La₂NiO_4+δ was investigated using Raman scattering. Magnetic and electronic Raman scattering in La₂NiO_4+δ with δ=0.02 and δ=0.15 has a large continuum below 1500 cm^-1. As temperature decreases to below 250 K at δ=0.15, the scattering intensity below 650 cm^-1 moves into the high-energy range and simultaneously the intensity at the energy of the undoped two-magnon peak increases, as expected from the separation of spin and charge densities. Similar effects are also observed even at the low carrier concentration of δ=0.02 below 150 K. This indicates that the spin and charge densities separate even at the low carrier concentration of δ=0.02.