Activation energies and localization in the fractional quantum Hall effect.

This paper summarizes an extensive study of the temperature dependence of magneto-transport in the fractional quantum Hall effect in GaAs-Al sub x Ga sub (1-x) As heterostructure devices of varying mobility and density. For devices with electron mobility 400,000 = mu = 1,000,000 cm sup 2 /Vs, we find a single activation energy, sup 3 DELTA/2, in the longitudinal transport coefficients, sigma sub (xx) and rho sub (xx) for Landau level filling factors nu = 1/3, 2/3, 4/3, and 5/3, with a magnetic field dependence which is vanishingly small for B ~ 5.5 T and increases to sup 3 DELTA ~ 6.8 K at B = 30 T. The observed sup 3 DELTA is more than a factor of three smaller than either the unbound quasi-particle/hole pair creation energy gap or the magneto-roton energy gap, calculated for an ideal two-dimensional electron system.