Exchange instabilities in electron systems: Bloch versus Stoner Ferromagnetism

TL;DR

This paper investigates how low-density 2D and 3D electron systems with Coulomb interactions can develop ferromagnetic instabilities due to exchange effects, with implications for low-disorder semiconductor systems.

Contribution

It identifies the critical densities for ferromagnetic instabilities of Stoner and Bloch types in electron systems and compares them to dispersion instability thresholds.

Findings

Ferromagnetic instabilities occur at densities higher than dispersion divergence.

Both Stoner and Bloch type instabilities are possible.

Implications for low-disorder 2D semiconductor systems are discussed.

Abstract

We show that 2D and 3D electron systems with the long-range Coulomb electron-electron interaction could develop ferromagnetic instabilities due to strong exchange effects at low densities. The critical densities in both 2D and 3D systems at which the magnetic instability, which could either be of Stoner type (second-order) or of Bloch type (first-order), are higher than the dispersion instability critical density where effective mass at the Fermi surface diverges. We discuss the theoretical as well as experimental implications of the ferromagnetic instability at low electron densities, particularly in low-disorder semiconductor-based two-dimensional systems.