Browsing by Author "Kono, K."

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Bound-bound transitions in the emission spectra of Ba+-He excimer
(2016-05-19)
Moroshkin, P.
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Kono, K.
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物理研究所
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Institute of Physics
We present an experimental and theoretical study of the emission and absorption spectra of the Ba+ ions and Ba+*He excimer quasimolecules in the cryogenic Ba-He plasma. We observe several spectral features in the emission spectrum, which we assign to the electronic transitions between bound states of the excimer correlating to the 6(2)P(3/2) and 5(2)D(3/2,5/2) states of Ba+. The resulting Ba+(5(2)D(J)) He is a metastable electronically excited complex with orbital angular momentum L = 2, thus expanding the family of known metal-helium quasimolecules. It might be suitable for high-resolution spectroscopic studies and for the search for new polyatomic exciplex structures.
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.
;
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.
Imaging and time-resolved study of laser-induced fluorescence of dysprosium atoms injected into superfluid helium
(2020-04-28)
Moroshkin, P.
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Kono, K.
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國際半導體學院
;
International College of Semiconductor Technology
We study the time evolution of the cloud of Dy atoms dispersed in superfluid helium and investigate the possibility of using these atoms as tracers for the imaging of superfluid-helium flows. The atoms are produced by pulsed laser ablation and are visualized via their laser-induced fluorescence. It turns out that the observation time is limited by the optical pumping of the atomic population into a nonabsorbing metastable state which is also responsible for the saturation of the fluorescence yield observed earlier.
Laser spectroscopy of phonons and rotons in superfluid helium doped with Dy atoms
(2018-03-09)
Moroshkin, P.
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Borel, A.
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Kono, K.
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物理研究所
;
Institute of Physics
We report the results of a high-resolution laser-spectroscopy study of dysprosium atoms injected into superfluid He-4. A special attention is paid to the transitions between the inner 4f and 5d electronic shells of Dy. The characteristic gap is observed between the zero-phonon line and the phonon wing in the experimental excitation spectrum that arises due to the peculiar structure of the phonon-roton spectrum of superfluid He. This observation resolves the longstanding discrepancy between the studies of bulk superfluid He and He nanodroplets.
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.
;
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.
;
Kono, K.
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物理研究所
;
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.
Observation of strong electron dephasing in highly disordered Cu93Ge4Au3 thin films
(2007-07-27)
Huang, S. M.
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Lee, T. C.
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Akimoto, H.
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Kono, K.
;
Lin, J. J.
We report the observation of strong electron dephasing in a series of disordered Cu93Ge4Au3 thin films. A very short electron dephasing time possessing very weak temperature dependence around 6 K, followed by an upturn with further decrease in temperature below 4 K, is found. The upturn is progressively more pronounced in more disordered samples. Moreover, a lnT-dependent, but high-magnetic-field-insensitive, resistance rise persisting from above 10 K down to 30 mK is observed in the films. These results suggest a nonmagnetic dephasing process which is stronger than any known mechanism and may originate from the coupling of conduction electrons to dynamic defects.
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.
;
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.
Spin blockade with spin singlet electrons
(2012-12-24)
Sun, Y. C.
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Amaha, S.
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Huang, S. M.
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Lin, J. J.
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Kono, K.
We observe a singlet spin blockade (SSB) in two-electron vertical double quantum dots where the single-electron transport is blocked for spin singlet electrons. In contrast to the conventional Pauli spin blockade with spin triplet electrons, this singlet spin blockade is observed under high magnetic field, where the doubly occupied states in one of the dots go beyond the singlet-triplet ground-state transition. The SSB region in Coulomb diamond measurements is in agreement with the two-electron excitation spectrum. A leakage current of 10 pA order is observed in SSB, consistent with the spin singlet lifetime due to random nuclear spin fluctuations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773304]
Spin Bottleneck in Resonance Tunneling through In0.04Ga0.96As/GaAs Vertical Double Quantum Dots
(2011-01-01)
Huang, S. M.
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Tokura, Y.
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Akimoto, H.
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Kono, K.
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Lin, J. J.
We study the electron resonance tunneling through double quantum dots with different g factors. We found that the resonance tunneling current is suppressed even if one of the Zeeman sublevels is aligned. The level broadening effect partially releases the blockade. The current maximum peak appears when the interdot detune is half of Zeeman energy difference of two quantum dots.
Spin Bottleneck in Resonant Tunneling through Double Quantum Dots with Different Zeeman Splittings
(2010-04-02)
Huang, S. M.
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Tokura, Y.
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Akimoto, H.
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Kono, K.
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Lin, J. J.
We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference.
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.
;
Scheer, E.
;
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.
Structural Transitions in a Quasi-1D Wigner Solid on Liquid Helium
(2016-01-01)
Beysengulov, N. R.
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Rees, D. G.
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Lysogorskiy, Yu.
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Galiullin, N. K.
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Vazjukov, A. S.
We present a detailed study of structural transitions of an electron system on liquid helium in quasi-1D confinement geometry. The structural transitions are experimentally observed as current oscillations in transport measurements with changing electrostatic confinement parameters. Finite element modelling and Monte Carlo simulations were used to investigate the electron configuration. With increasing electron density, the single chain of electrons splits into a two-, three- and so on row configuration. A proliferation of defects accompanies each structural transition. We find a good agreement between the observed current modulation and the evolution of the electron row configuration predicted by our calculations.
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.
;
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.
Transport of Electrons on Liquid Helium in a Microchannel Device near the Current Threshold
(2016-09)
Beysengulov, N. R.
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Rees, D. G.
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Tayurskii, D. A.
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Kono, K.
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物理研究所
We study the transport of strongly interacting electrons on the surface of liquid helium confined in a microchannel geometry, near the current threshold point. The current threshold depends on the electrostatic confinement, created by the microchannel electrodes, and on the electrostatic potential of electron system. Depending on the geometry of the microchannel, the current pinch-off can occur at the center or move to the edges of the microchannel, as confirmed by Finite Element Model calculations. The confining potential dependence of electron conductivity above the current threshold point is consistent with a classical charge continuum model. However, we find that below the threshold point electron transport is suppressed due to charging energy effects.
Trapping of metallic nanoparticles under the free surface of superfluid helium in a static electric field
(2019-07-01)
Moroshkin, P.
;
Leiderer, P.
;
Moeller, Th. B.
;
Kono, K.
;
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.