The width of AC quantum Hall plateaus

The quantum Hall effect in GaAs heterostructures is investigated with alternating currents in the kilohertz frequency range. The width of the plateau shows no significant frequency dependence and is determined by an effective temperature. This effective temperature is higher than the bath temperature by an amount which depends on the current and the bath temperature. Whereas the electron temperature determined by other measurements of the dc conductivity shows a clear divergence toward the centre of the Landau levels, the effective temperature determined from the ac plateau width does not depend on the noninteger fraction of the filling factor [1], [2]. This unexpected result is now explained as a matter of the definition of the effective temperature and not of unexpected physics.