Inequivalence of the low-density insulating state and quantum Hall insulating states in a strongly correlated two-dimensional electron system

We find that the behaviors of the voltage-current characteristics as one enters the low-density insulating state and integer quantum Hall insulating states in the ultraclean two-dimensional electron system in SiGe/Si/SiGe quantum wells are qualitatively different. The double-threshold voltage-current curves, representative of the electron solid formation at low densities, are not observed in the quantum Hall regime, which does not confirm the existence of a quasiparticle quantum Hall Wigner solid and indicates that quasiparticles near integer filling do not form an independent subsystem.