  Disorder and electron-electron interaction play essential roles in the
physics of electron systems in condensed matter. In two-dimensional, quantum
Hall systems, extensive studies of disorder-induced localization have led to
the emergence of a scaling picture with a single extended state, characterized
by a power-law divergence of the localization length in the zero-temperature
limit. Experimentally, scaling has been investigated via measuring the
temperature dependence of plateau-to-plateau transitions between the integer
quantum Hall states (IQHSs), yielding a critical exponent $\kappa\simeq 0.42$.
Here we report scaling measurements in the fractional quantum Hall state (FQHS)
regime where interaction plays a dominant role. Our study is partly motivated
by recent calculations, based on the composite fermion theory, that suggest
identical critical exponents in both IQHS and FQHS cases to the extent that the
interaction between composite fermions is negligible. The samples used in our
experiments are two-dimensional electron systems confined to GaAs quantum wells
of exceptionally high quality. We find that $\kappa$ varies for transitions
between different FQHSs observed on the flanks of Landau level filling factor
$\nu=1/2$, and has a value close to that reported for the IQHS transitions only
for a limited number of transitions between high-order FQHSs with intermediate
strength. We discuss possible origins of the non-universal $\kappa$ observed in
our experiments.
