Using a novel technique, we make quantitative measurements of the spin polarization of dilute (3.4 to 6.8*10^{10} cm^{-2}) GaAs (311)A two-dimensional holes as a function of an in-plane magnetic field. As the field is increased the system gradually becomes spin polarized, with the degree of spin polarization depending on the orientation of the field relative to the crystal axes. Moreover, the behavior of the system turns from metallic to insulating \textit{before} it is fully spin polarized. The minority-spin population at the transition is ~8*10^{9} cm^{-2}, close to the density below which the system makes a transition to an insulating state in the absence of a magnetic field.
@article{arxiv.cond-mat/0012128,
title = {In-plane magnetic field-induced spin polarization and transition to insulating behavior in two-dimensional hole systems},
author = {E. Tutuc and E. P. De Poortere and S. J. Papadakis and M. Shayegan},
journal= {arXiv preprint arXiv:cond-mat/0012128},
year = {2009}
}