Contactless Measurement of AC Conductance in Quantum Hall Structures

TL;DR

This paper introduces a combined, contactless method using acoustic and microwave spectroscopy to measure the frequency-dependent conductance of quantum Hall structures across a broad frequency range, validated on a heterostructure.

Contribution

It presents a novel procedure that integrates two known probeless techniques to determine quantum Hall conductance over a wide frequency spectrum.

Findings

The method accurately measures conductance in quantum Hall structures.

Conductance at maxima of magnetic field dependence remains frequency independent.

Procedure is validated on a p-SiGe/Ge/SiGe heterostructure.

Abstract

We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods -- acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized $p$-SiGe/Ge/SiGe heterostructure.