Itinerant Electron Ferromagnetism in the Quantum Hall Regime

TL;DR

This paper investigates the temperature and magnetic field dependence of ferromagnetism in a 2D electron gas at Landau level filling factor ν=1, emphasizing electron itinerancy and spin-wave interactions, and compares theoretical predictions with experimental data.

Contribution

It introduces a Green's function approach incorporating spin-wave interactions beyond Hartree-Fock to better describe finite-temperature properties of quantum Hall ferromagnets.

Findings

Predicted a sharp tunneling conductance peak at large bias proportional to temperature.

Calculated temperature dependence of spin magnetization and nuclear spin relaxation rate.

Compared theoretical results with experimental data and other models.

Abstract

We report on a study of the temperature and Zeeman-coupling-strength dependence of the one-particle Green's function of a two-dimensional (2D) electron gas at Landau level filling factor $\nu =1$ where the ground state is a strong ferromagnet. Our work places emphasis on the role played by the itinerancy of the electrons, which carry the spin magnetization and on analogies between this system and conventional itinerant electron ferromagnets. We discuss the application to this system of the self-consistent Hartree-Fock approximation, which is analogous to the band theory description of metallic ferromagnetism and fails badly at finite temperatures because it does not account for spin-wave excitations. We go beyond this level by evaluating the one-particle Green's function using a self-energy, which accounts for quasiparticle spin-wave interactions. We report results for the temperature dependence of the spin magnetization, the nuclear spin relaxation rate, and 2D-2D tunneling conductances. Our calculations predict a sharp peak in the tunneling conductance at large bias voltages with strength proportional to temperature. We compare with experiment, where available, and with predictions based on numerical exact diagonalization and other theoretical approaches.