EXPERIMENTAL-STUDY OF SIGMA(XX)(T) FOR QUASI-PARTICLE CHARGE DETERMINATION IN THE FRACTIONAL QUANTUM HALL-EFFECT

The temperature dependence of the diagonal conductivity, sigma(xx)(T), at integer and fractional quantum Hall effect (FQHE) minima was measured in a sample at various densities. We find sigma(xx)c, the 1/T --> 0 extrapolated value of sigma(xx)(T) from Arrhenius plots, is different for different densities. While a reasonable (1/q)2 scaling of sigma(xx)c at the filling factors nu = p/q is observed at lower densities, the scaling is not seen in the highest density data. We explain this loss of scaling by a breakdown of the assumption for a simple activated formula caused by a crossover between the extended state width, GAMMA, and T for the measurement. For kT > GAMMA, the scaling of the 1/T intercept is recovered by plotting sigma(xx)(T) X T vs 1/T and fitting to sigma(xx)(T) = (sigma(xx)*c/T)exp(-DELTAE/kT). We attribute the (1/q)2 scaling in sigma(xx)c and sigma(xx)*c observed at each density to a (1/q)2 scaling in the T = 0 conductivity. This supports the assertion of Clark et al. that the charge e* of the quasiparticle excitation from the FQHE ground state at nu = p/q can be determined from sigma(xx)(T) and the charge is e* = e/q.