Experimental study of σxx(T) for quasiparticle charge determination in the fractional quantum Hall effect

The temperature dependence of the diagonal conductivity, σxx(T), at integer and fractional quantum Hall effect (FQHE) minima was measured in a sample at various densities. We find σxxc, the 1/T→0 extrapolated value of σxx(T) from Arrhenius plots, is different for different densities. While a reasonable (1/q)2 scaling of σxxc at the filling factors ν=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, Γ, and T for the measurement. For kT>Γ, the scaling of the 1/T intercept is recovered by plotting σxx(T)×T vs 1/T and fitting to σxx(T)=(σxx*c/T)exp(-ΔE/kT). We attribute the (1/q)2 scaling in σxxc and σxx*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 ν=p/q can be determined from σxx(T) and the charge is e*=e/q.