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

We study the ν=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=0–7.6×1011 cm−2 with a peak mobility μ=5.5×106 cm2 Vs−1. The ν=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 ν=5/2.