Probing Spontaneous Spin Magnetization and Two-Phase State in Two-Dimensional Correlated Electron System

Abstract

Strongly interacting two-dimensional (2D) carrier system has a tendency to spontaneous spin magnetization and mass divergence. Numerous experiments aimed to reveal these instabilities were not entirely convincing. In particular, spin susceptibility of itinerant electrons, determined from quantum oscillations, remains finite at the critical density of the 2D metal-insulator transition (MIT), n = nc. In contrast, the susceptibility and effective mass determined from high field magnetotransport were reported to diverge. Later, it became clear that as interactions grow, the homogeneous 2D Fermi liquid breaks into a two phase state which hampers interpretation of the experimental data. The thermodynamic magnetization measurements have revealed spontaneous formation of the spin-polarized collective electron droplets (“nanomagnets”) in the correlated 2D Fermi liquid, while the spin susceptibility of itinerant electrons in the surrounding 2D “Fermi sea” remains finite. Here, we report how the non Fermi-liquid two-phase state (dilute ferromagnet) reveals itself in magnetotransport and zero field transport. We found in the correlated 2D system a novel energy scale T∗<TF. At T≈T∗ the in-plane field magnetotransport and zero field transport exhibit features. Finally, in thermodynamic magnetization, the spin susceptibility per electron, ∂χ/∂n changes sign at T≈T∗. All three notable temperatures are close to each other, behave critically, \( \propto (n-n_{c})\); we associate, therefore, T∗ with a novel energy scale caused by interactions in the two-phase 2DE system.