Effects of metallic gates on ac measurements of the quantum hall resistance

Abstract

Using a sample with a split back-gate, a linear frequency dependence of the ac quantum Hall resistance was observed. The frequency coefficient, which is due to dielectric losses produced by leakage current between the 2DEG and the back-gates, can be turned from a positive to a negative values by increasing the back-gate voltage. More interestingly, by removing theses back-gates, the losses can be considerably reduced leading to a residual frequency coefficient on the order of (0.03±0.03)·10−6 /kHz. Moreover, at 1 kHz, an extremely flat plateau was observed over a magnetic field range of 1.4 T. These results clearly indicate that the audio frequency dependence of the QHR is to a large extend related to the measurement apparatus and does not originate from the physical transport properties of the 2DEG.

Compendium for precise ac measurements of the quantum Hall resistance

“…Another reason for this progress was an improved understanding of the effect of gates [6][7][8]. In general, a gate, and other conductors close to the QHE device, act as parasitic capacitive electrodes and increase the frequency-and current-dependent effects [8].…”

“…Another reason for this progress was an improved understanding of the effect of gates [6][7][8]. In general, a gate, and other conductors close to the QHE device, act as parasitic capacitive electrodes and increase the frequency-and current-dependent effects [8]. An approximate solution to this intrinsic problem is to avoid all metals close to the QHE device and then to correct for the internal and the residual external effects [5,12].…”

“…The crucial role of the capacitive device environment requires special attention when mounting the device. The choice we recommend is the standardized mounting system used in EU-ROMET project 540 [8]. That system employs a metal case and coaxial leads.…”

“…After the first precision ac measurement of the QHR had demonstrated an accuracy of a few parts in 10 6 [4], considerable progress has been made on the subject of accurate ac QHR measurements [5][6][7][8][9][10][11][12][13][14][15]. Today, measurements with carefully set up ac bridges achieve an uncertainty of a few parts in 10 8 , and agreement at this level has been achieved between different NMIs.…”

Digitally assisted coaxial bridge for automatic quantum Hall effect measurements at audio frequencies

“…The investigation of the Quantum Hall Effect (QHE) requires the use of coaxial ac bridges to compare the Quantum Hall Resistance (QHR) to calculable resistance standards at audio frequencies [1], [2], [3]. Such dedicated bridges are optimized to give the highest accuracy in impedance comparison [4].…”