Browsing by Author "Shaban, F."

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Pulsed transport of electrons on liquid helium confined in narrow channels
(2014-01-01)
Shaban, F.
;
Lorenz, T.
;
Rau, R.
;
Ashari, M.
;
Rees, D.
We have used a Source-Gate-Drain configuration with electrons on liquid helium ( the Helium Field Effect Transistor "He-FET") to study the transport of "classical" electrons through narrow channels. The channels, formed by the split gate of the device, were between ten and a hundred mu m long and several mu m wide, and could be blocked completely by a negative bias voltage applied to the gate. In contrast to previous experiments, where the electron densities in source and drain were nearly the same and the system therefore was close to equilibrium, in the present measurement the drain was empty. The transport of the electrons through the channel was initiated by opening the gate with a short positive pulse with a duration down to nanoseconds, and the amount of electrons which passed during this time was registered. In this way, we could determine for the first time the transport properties of such a system on a nanosecond time scale and far off equilibrium. Measurements with varying gate voltage provide clear evidence for the formation of lanes of electrons in the channels.
The Helium Field Effect Transistor (II): Gated Transport of Surface-State Electrons Through Micro-constrictions
(2016-11)
Shaban, F.
;
Ashari, M.
;
Lorenz, T.
;
Rau, R.
;
Scheer, E.
We present transport measurements of surface-state electrons on liquid helium films in confined geometry. The measurements are taken using split-gate devices similar to a field effect transistor. The number of electrons passing between the source and drain areas of the device can be precisely controlled by changing the length of the voltage pulse applied to the gate electrode. We find evidence that the effective driving potential depends on electron-electron interactions, as well as the electric field applied to the substrate. Our measurements indicate that the mobility of electrons on helium films can be high and that microfabricated transistor devices allow electron manipulation on length scales close to the interelectron separation. Our experiment is an important step toward investigations of surface-state electron properties at much higher densities, for which the quantum melting of the system to a degenerate Fermi gas should be observed.