Suppression of gate screening on edge magnetoplasmons by highly resistive ZnO gate

We investigate a way to suppress high-frequency coupling between a gate and low-dimensional electron systems in the gigahertz range by measuring the velocity of edge magnetoplasmons (EMPs) in InAs quantum Hall systems. We compare the EMP velocity in three samples with different electromagnetic environments-one has a highly resistive zinc oxide (ZnO) top gate, another has a normal metal (Ti/Au) top gate, and the other does not have a gate. The measured EMP velocity in the ZnO gate sample is one order of magnitude larger than that in the Ti/Au gate sample and almost the same as that in the ungated sample. As is well known, the smaller velocity in the Ti/Au gate sample is due to the screening of the electric field in EMPs. The suppression of the gate screening effect in the ZnO gate sample allows us to measure the velocity of unscreened EMPs while changing the electron density. It also offers a way to avoid unwanted high-frequency coupling between quantum Hall edge channels and gate electrodes.