Mass enhancement versus Stoner enhancement in strongly correlated metallic perovskites:LaNiO3andLaCuO3

Measurements of physical properties, including transport and magnetic properties, specific heat, and thermal conductivity, have been performed on high-quality samples of ${\mathrm{LaNiO}}_3$ and ${\mathrm{LaCuO}}_3$ synthesized under high pressure. Some measurements, such as thermoelectric power and magnetic susceptibility, have been made under high pressure. The availability of a complete set of data enables a side-by-side comparison between these two narrowband systems. We have demonstrated unambiguously the mass enhancement due to electron-electron correlations in both systems relative to the recent density functional theory results. Correlations in these narrowband systems also enhance the magnetic susceptibility. Ferromagnetic spin fluctuations give rise to a strong Stoner enhancement in the magnetic susceptibility in the quarter-filled ${\mathrm{LaNiO}}_3$. Although we are able to tune the bandwidth by either chemical substitutions or by applying hydrostatic pressure on ${\mathrm{LaNiO}}_3$, the Stoner enhancement does not lead to the Stoner instability.