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Register a new userInhomogeneous screening of gate electric field by interface states in graphene FETs
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The electronic states at graphene-SiO$_2$ interface and their inhomogeneity was investigated using the back-gate-voltage dependence of local tunnel spectra acquired with a scanning tunneling microscope. The conductance spectra show two, or occasionally three, minima that evolve along the bias-voltage axis with the back gate voltage. This evolution is modeled using tip-gating and interface states. The energy dependent interface states density, $D_{it}(E)$, required to model the back-gate evolution of the minima, is found to have significant inhomogeneity in its energy-width. A broad $D_{it}(E)$ leads to an effect similar to a reduction in the Fermi velocity while the narrow $D_{it}(E)$ leads to the pinning of the Fermi energy close to the Dirac point, as observed in some places, due to enhanced screening of the gate electric field by the narrow $D_{it}(E)$
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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.
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