  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 EMPvelocity 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.
