Probing spin susceptibility of a correlated two-dimensional electron system by transport and magnetization measurements

We report temperature and density dependences of the spin susceptibility of strongly interacting electrons in Si inversion layers. We measured (i) the itinerant electron susceptibility $\chi^*$ from the Shubnikov-de Haas oscillations in crossed magnetic fields and (ii) thermodynamic susceptibility $\chi_{\rm T}$ sensitive to all the electrons in the layer. Both $\chi^*$ and $\chi_{\rm T}$ are strongly enhanced with lowering the electron density in the metallic phase. However, there is no sign of divergency of either quantity at the density of the metal-insulator transition $n_c$. Moreover, the value of $\chi_{\rm T}$, which can be measured across the transition down to very low densities deep in the insulating phase, increases with density at $n<n_c$, as expected. In the absence of magnetic field, we found the temperature dependence of $\chi^*$ to be consistent with Fermi-liquid-based predictions, and to be much weaker than the power-law, predicted by non-Fermi-liquid models. We attribute a much stronger temperature dependence of $\chi_{\rm T}$ to localized spin droplets. In strong enough in-plane magnetic field, we found the temperature dependence of $\chi^*$ to be stronger than that expected for the Fermi liquid interaction corrections.