Spontaneous spin polarization in doped semiconductor quantum wells

TL;DR

This paper investigates the conditions under which a ferromagnetic phase transition occurs in doped GaAs/AlGaAs quantum wells, emphasizing the influence of well width and exchange interactions on the critical density.

Contribution

It provides a theoretical analysis of the dependence of ferromagnetic transition on well width and introduces a model predicting transition conditions in narrow quantum wells.

Findings

Existence of a critical well width for ferromagnetic transition.

Transition can occur at lower electron densities in narrow wells.

Transition depends on the interplay of exchange interaction components.

Abstract

We calculate the critical density of the zero-temperature, first-order ferromagnetic phase transition in n-doped GaAs/AlGaAs quantum wells. We find that the existence of the ferromagnetic transition is dependent upon the choice of well width. We demonstrate rigorously that this dependence is governed by the interplay between different components of the exchange interaction and that there exists an upper limit for the well width beyond which there is no transition. We predict that some narrow quantum wells could exhibit this transition at electron densities lower than the ones that have been considered experimentally thus far. We use a screened Hartree-Fock approximation with a polarization-dependent effective mass, which is adjusted to match the critical density predicted by Monte Carlo calculations for the two-dimensional electron gas.