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Influence of voltmeter impedance on quantum Hall measurements

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2 Author(s)
Fischer, F. ; Walter Schottky Institut, Technische Universität München, Garching 85748, Germany ; Grayson, M.

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We report the influence of voltmeters on measurements of the longitudinal resistance Rxx in the quantum Hall-effect regime. We show that for input resistances typical of standard digital lock-in amplifiers, Rxx can show a nonzero minimum which might be mistaken for a parallel conduction in the doping layer. This residual impedance at the Rxx minima can be calculated with Zres=Rxy2/Rin+jωCRxy2, where Rin is the input resistance of the voltmeter, C is the measurement capacitance, and Rxy=h/νe2 is the Hall resistance. In contrast to a real parallel conduction, the effect disappears when either the current source and ground contact are swapped or the polarity of the magnetic field is changed; examples with data are shown. We discuss how proper phasing of a lock-in amplifier is necessary to eliminate false residual minima which arise from stray capacitances.

Published in:

Journal of Applied Physics  (Volume:98 ,  Issue: 1 )