Theory of spin-singlet fractional quantum Hall effect at ν=1/2

Motivated by the observation of fractional quantum Hall effect (FQHE) at filling factor ν=2+1/2 by Willett et al., we investigate the nature of the spin-singlet FQHE at ν=1/2. We show that a simple trial wave function for the ν=1/2 state, proposed earlier by one of us, is the exact nondegenerate ground state of a hard-core interaction model, and provide numerical evidence that it is adiabatically connected to the true Coulomb ground state.