Fractional Quantum Hall effect in extremely high mobility GaAs- (AlGa)As heterostructures.

Proc. of EP2DS Conference, Sante Fe, New Mexico, July 27-31, 1987. The fractional quantum Hall effect (FQHE) is now understood as resulting from a correlated liquid with quasiparticle excitations separated from the grounds state by a finite energy gap. 

These gaps are measured in transport experiments by determining activation energies of the transport coefficients rho sub (chi chi) or sigma sub (chi chi).