Evidence of breakdown of the spin symmetry in diluted 2D electron gases

TL;DR

This paper presents experimental and theoretical evidence for the breakdown of spin symmetry and the emergence of ferromagnetism in dilute two-dimensional electron gases, highlighting the role of exchange interactions and collective excitations.

Contribution

It demonstrates the breakdown of spin symmetry and the onset of ferromagnetism in dilute 2DEGs through inelastic light scattering and advanced calculations.

Findings

Enhanced exchange and correlation energies at low densities

Evidence of ferromagnetic ground state in dilute 2DEG

Breakdown of spin symmetry observed

Abstract

Recent claims of an experimental demonstration of spontaneous spin polarisation in dilute electron gases \cite{young99} revived long standing theoretical discussions \cite{ceper99,bloch}. In two dimensions, the stabilisation of a ferromagnetic fluid might be hindered by the occurrence of the metal-insulator transition at low densities \cite{abra79}. To circumvent localisation in the two-dimensional electron gas (2DEG) we investigated the low populated second electron subband, where the disorder potential is mainly screened by the high density of the first subband. This letter reports on the breakdown of the spin symmetry in a 2DEG, revealed by the abrupt enhancement of the exchange and correlation terms of the Coulomb interaction, as determined from the energies of the collective charge and spin excitations. Inelastic light scattering experiments and calculations within the time-dependent local spin-density approximation give strong evidence for the existence of a ferromagnetic ground state in the diluted regime.