EXPERIMENTAL-DETERMINATION OF THE TRANSPORT-PROPERTIES OF COMPOSITE FERMIONS WITH REDUCED LANDE G-FACTOR

We demonstrate experimentally the existence of unpolarized spin states of composite fermions in the fractional quantum Hall effect regime. T he modulus of the effective Lande g-factor was reduced using hydrostat ic pressure and the transport properties of the first and second hiera rchy of composite fermion states were studied in an AlGaAs/GaAs hetero junction in perpendicular magnetic fields. The activation energy of st ates at filling factor, nu = 2/3 and 2/5 show a variation with effecti ve Lande g-factor that is consistent with a spin-unpolarized ground st ate at these filling factors. The rapid destruction of the energy gap in the first composite fermion hierarchy at nu = 2/5 follows the press ure dependence of the effective Lande g-factor of free electrons in Ga As. We show that structure in sigma(xx) initially absent at ambient pr essure, develops at even filling factor fractions corresponding to met allic states at nu = 3/8 and nu = 5/12 under reduced Lande g-factor co nditions. Consistent behaviour is observed independent of the carrier density in the dilute electron system at 4.4 x 10(10) and 6.8 x 10(10) cm-2.