NMR Determination of 2D Electron Spin Polarization at $\nu=1/2$

TL;DR

This study uses NMR spin-echo techniques to measure the spin polarization of 2D electrons at filling factor 1/2 in GaAs quantum wells, revealing that a non-interacting composite fermion model explains the data well, with some limitations under tilted magnetic fields.

Contribution

It introduces a method to determine 2D electron spin polarization via NMR hyperfine shifts and applies it to analyze the behavior at ν=1/2, supporting a simple composite fermion model.

Findings

Spin polarization at ν=1/2 is well described by a non-interacting composite fermion model.

Temperature and magnetic field dependencies of spin polarization are characterized.

Some inconsistencies appear when the magnetic field is tilted, indicating limitations of the model.

Abstract

Using a `standard' NMR spin-echo technique we determined the spin polarization of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei in the wells. Concentrating on the temperature and magnetic field dependencies of spin polarization at Landau level filling factor $\nu =1/2$, we find that the results are described well by a simple model of non-interacting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.