Experimental determination of the transport properties of composite fermions with reduced Lande g-factor

Abstract

We demonstrate experimentally the existence of unpolarized spin states of composite fermions in the fractional quantum Hall effect regime. The modulus of the effective Lande g-factor was reduced using hydrostatic pressure and the transport properties of the first and second hierarchy of composite fermion states were studied in an AlGaAs/GaAs heterojunction in perpendicular magnetic fields. The activation energy of states at filling factor, nu =2/3 and 2/5 show a variation with effective Lande g-factor that is consistent with a spin-unpolarized ground state at these filling factors. The rapid destruction of the energy gap in the first composite fermion hierarchy at nu =2/5 follows the pressure dependence of the effective Lande g-factor of free electrons in GaAs. We show that structure in sigma xx, initially absent at ambient pressure, develops at even filling factor fractions corresponding to metallic states at nu =3/8 and nu =5/12 under reduced Lande g-factor conditions. Consistent behaviour is observed independent of the carrier density in the dilute electron system at 4.4*1010 and 6.8*1010 cm-2.