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

We apply polarization resolved photoluminescence spectroscopy to measure the spin polarization of a two dimensional electron gas in perpendicular magnetic field. We find that the splitting between the sigma(+) and sigma(-) polarizations exhibits a sharp drop at v = 5/2 and is equal to the bare Zeeman energy, which resembles the behavior at even filling factors. We show that this behavior is consistent with filling factor v = 5/2 being unpolarized.