Optical Probing of the Spin Polarization of the nu=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. In the vicinity of filling factor nu=5/2, we observe a sharp discontinuity in the energy of the zero Landau level emission line. We find that the splitting between the two circular polarizations exhibits a sharp drop at nu=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 nu=5/2 being unpolarized.