MAGNETOCAPACITANCE IN QUANTUM HALL REGIME WITH EXTERNAL DC CURRENT

We have investigated the magnetocapacitance between Sates and two dime nsional electron system in a GaAs/AlGaAs heterostructure with an exter nal de current at quantum Hall (QH) plateau regime. With increasing de current, the minimum values of capacitance at QH plateaux increase an d the range of magnetic fields showing the capacitance minima decrease s. The electrons excited by the external de current enhance the sigma( xx) which causes the breakdown of the QH effect. In a certain magnetic field and current direction, the capacitance dip at QH plateau splits into two valleys with de current. These results are considered to be due to the change of effective gate voltage caused by the current. The breakdown current of the QH effect evaluated by the resistance measur ement is several times larger than that obtained by the de current dep endence of the magnetocapacitance, since the capacitance is very sensi tive to the residual sigma(xx) The vanishing of the capacitance minima may be the precursor of QH breakdown. (C) 1998 Elsevier Science Ltd. All rights reserved.