NMR Probing of the Spin Polarization of the v=5/2 Quantum Hall State

Resistively detected nuclear magnetic resonance is used to measure the Knight shift of the As-75 nuclei and determine the electron spin polarization of the fractional quantum Hall states of the second Landau level. We show that the 5/2 state is fully polarized within experimental error, thus confirming a fundamental assumption of the Moore-Read theory. We measure the electron heating under radio frequency excitation and show that we are able to detect NMR at electron temperatures down to 30 mK.