NMR investigation of how free composite fermions are at ν = 1/2

The measurements of the electron spin polarization were performed on a two dimensional system by using NMR method. The imbalance of spin-up and spin-down composite fermions was mapped as a function of Zeeman effect. It was shown that the dependence of integer quantum Hall state around half-filling violated the particle-hole symmetry for partially polarized Fermi state.