The Spin Polarization at the Metal-Insulator Transition

We have extracted the spin-polarized (SP) density of states (DOS) of 3-dimensional amorphous (a-) Gd$_{x}$Si$_{1-x}$ in the quantum critical regime (QCR) of a magnetic field tunable metal-insulator transition (MIT) by measuring the SP tunneling conductance of an Al/Al$_{2}$O$_{3}$/a-Gd$_{x}$Si$_{1-x}$ planar tunnel junction at T=25mK and H$\le $3.0T. We have applied SP Abrikosov-Gorkov DOS to fit the data, leading to a significant improvement over prior attempts to use a SP Bardeen-Cooper-Schrieffer DOS. We find a large polarization near the MIT of a-Gd$_{x}$Si$_{1-x}$ (x=0.14). We have determined polarization values at different applied magnetic fields allowing for a study of the polarization dependence in the QCR.