Browsing by Author "Leiderer, P."

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Dynamics of the Vortex-Particle Complexes Bound to the Free Surface of Superfluid Helium
(2019-05-03)
Moroshkin, P.
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Leiderer, P.
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Kono, K.
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Inui, S.
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Tsubota, M.
We present an experimental and theoretical study of the 2D dynamics of electrically charged nanoparticles trapped under a free surface of superfluid helium in a static vertical electric field. We focus on the dynamics of particles driven by the interaction with quantized vortices terminating at the free surface. We identify two types of particle trajectories and the associated vortex structures: vertical linear vortices pinned at the bottom of the container and half-ring vortices traveling along the free surface of the liquid.
Metallic nanowires and mesoscopic networks on a free surface of superfluid helium and charge-shuttling across the liquid-gas interface
(2016-10-14)
Moroshkin, P.
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Batulin, R.
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Leiderer, P.
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Kono, K.
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物理研究所
We investigate the motion of electrically charged metallic nano- and microparticles produced by laser ablation in He gas and injected into superfluid helium. In the presence of a vertical static electric field, the particles either perform a repetitive shuttle-like motion transporting the charge across the liquid-gas interface or become trapped under the free surface of liquid He and coalesce into long filaments and complex two-dimensional mesoscopic networks. A classical electrohydrodynamic model is used to describe the motion of charged microparticles in superfluid He. The resulting filaments and networks are analyzed using electron microscopy. It is demonstrated that each filament is in fact composed of a large number of nanowires with a characteristic diameter of order of 10 nm and extremely large aspect ratios.
Motion of metallic microparticles in superfluid helium in the presence of space charge
(2017-04-01)
Moroshkin, P.
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Leiderer, P.
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Kono, K.
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物理研究所
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Institute of Physics
We report an experimental and theoretical study of the motion of metallic micro-and nanoparticles in cryogenic superfluid helium in the presence of a static electric field. Depending on the polarity of the applied field, the system is charged with a large number of positive ions or free electrons. For the electrons, we observe the formation of a negative charge layer above the free surface of liquid He and a shuttle-like motion of metallic particles between this layer and the positively charged bottom electrode. For the positive ions, the positive space charge is created in the liquid and the particle motion resembles bouncing off the (negatively charged) bottom electrode. The observations are explained by a theoretical model based on classical electrostatics and hydrodynamics. Published by AIP Publishing.
Perturbations of a Free Surface of Superfluid Helium by the Ion Wind Produced by a Corona Discharge Above the Liquid
(2019-05-01)
Moroshkin, P.
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Leiderer, P.
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Kono, K.
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電子物理學系
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Department of Electrophysics
We report on experimental observations of the deformations of a free surface of superfluid 4He in the presence of the corona discharge above the liquid. The effect is attributed to the impact of the ion wind generated by the discharge.
Pulsed transport of electrons on liquid helium confined in narrow channels
(2014-01-01)
Shaban, F.
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Lorenz, T.
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Rau, R.
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Ashari, M.
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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.
Stability of Surface State Electrons on Helium Films
(2016-05)
Leiderer, P.
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Scheer, E.
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Kono, K.
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Lin, J. -J.
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Rees, D. G.
Electrons on helium substrates form a model Coulomb system in which the transition from classical electron liquid to Wigner crystal is readily observed. However, attempts to increase the electron density in order to observe the \'quantum melting\' of the system to a Fermi degenerate gas are hindered by an instability of the helium surface. Here we describe experimental efforts to reach the degenerate regime on thin helium films and microstructured substrates, for which the surface instability is suppressed. We demonstrate that, although the electron densities obtained exceed those for bulk helium substrates, observation of quantum melting remains challenging. We discuss possible solutions to the technical challenges involved.
Stability of Surface State Electrons on Helium Films
(2016-05-01)
Leiderer, P.
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Scheer, E.
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Kono, K.
;
Lin, J. -J.
;
Rees, D. G.
Electrons on helium substrates form a model Coulomb system in which the transition from classical electron liquid to Wigner crystal is readily observed. However, attempts to increase the electron density in order to observe the 'quantum melting' of the system to a Fermi degenerate gas are hindered by an instability of the helium surface. Here we describe experimental efforts to reach the degenerate regime on thin helium films and microstructured substrates, for which the surface instability is suppressed. We demonstrate that, although the electron densities obtained exceed those for bulk helium substrates, observation of quantum melting remains challenging. We discuss possible solutions to the technical challenges involved.
Taylor cone and electrospraying at a free surface of superfluid helium charged from below
(2017-05-19)
Moroshkin, P.
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Leiderer, P.
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Moeller, Th. B.
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Kono, K.
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物理研究所
Electrically charged metallic micro-and nanoparticles are trapped under a free surface of superfluid He in a vertical static electric field. We observe a static deformation of the charged liquid surface in the form of a Taylor cone and the emission of a charged liquid helium jet (electrospray). Our numeric calculations reproduce the static shape of the cone.
The Helium Field Effect Transistor (II): Gated Transport of Surface-State Electrons Through Micro-constrictions
(2016-11)
Shaban, F.
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Ashari, M.
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Lorenz, T.
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Rau, R.
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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.
Trapping of metallic nanoparticles under the free surface of superfluid helium in a static electric field
(2019-07-01)
Moroshkin, P.
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Leiderer, P.
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Moeller, Th. B.
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Kono, K.
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國際半導體學院
Electrically charged metallic microparticles and nanoparticles have been trapped under a free surface of superfluid He-4 in a vertical static electric field. We report the details of the trapping technique and the observed dynamics of the trapped particles moving along the surface and driven by surface waves, by a static horizontal electric field, and by a thermal counterflow within the surface layer of liquid He.