Experimental evidence for a spin-polarized ground state in the nu=5/2 fractional quantum Hall effect

We study the v = 5/2 even-denominator fractional quantum Hall effect (FQHE) over a wide range of magnetic field in a heterojunction insulated gate field-effect transistor (HIGFET). The electron density can be tuned from n = 0-7.6 X 10(11) Cm-2 with a peak mobility mu = 5.5 X 10(6) cm(2) Vs(-1). The v = 5/2 state shows a strong minimum in diagonal resistance and a developing Hall plateau at magnetic fields (B) as high as 12.6 T. The strength of the energy gap varies smoothly with B-field. We interpret these observations as strong evidence for a spin-polarized ground state at v = 5/2. (C) 2001 Elsevier Science Ltd. All rights reserved.