Magnetic Field Induced Spin Polarization of AlAs Two-dimensional Electrons

TL;DR

This study investigates the spin polarization of 2D electrons in AlAs under in-plane magnetic fields, revealing a linear relationship between polarization field and electron density, with implications for the effective g-factor and mass.

Contribution

It provides the first detailed measurements of spin polarization in AlAs 2D electrons, showing the product |g*|m* is density-independent and enhanced, contrasting with Si-MOSFET results.

Findings

Polarization field B_P increases linearly with electron density.

The product |g*|m* remains constant and is enhanced by a factor of ~4.

No divergence of |g*|m* as density approaches zero.

Abstract

Two-dimensional (2D) electrons in an in-plane magnetic field become fully spin polarized above a field B_P, which we can determine from the in-plane magnetoresistance. We perform such measurements in modulation-doped AlAs electron systems, and find that the field B_P increases approximately linearly with 2D electron density. These results imply that the product |g*|m*, where g* is the effective g-factor and m* the effective mass, is a constant essentially independent of density. While the deduced |g*|m* is enhanced relative to its band value by a factor of ~ 4, we see no indication of its divergence as 2D density approaches zero. These observations are at odds with results obtained in Si-MOSFETs, but qualitatively confirm spin polarization studies of 2D GaAs carriers.