Energy Gap and Spin Polarization in the 5/2 Fractional Quantum Hall Effect

We consider the issue of the appropriate underlying wavefunction describing the enigmatic 5/2 fractional quantum Hall effect (FQHE), the only even denominator FQHE unambiguously observed in a single layer two dimensional (2D) electron system. Using experimental transport data and theoretical analysis, we argue that the possibility of the experimental 5/2 FQH state being not fully spin-polarized cannot be ruled out. We also establish that the parallel field-induced destruction of the 5/2 FQHE arises primarily from the enhancement of effective disorder by the parallel field with the Zeeman energy playing an important quantitative role.