Browsing by Author "Ikegami, Hiroki"

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Melting of Wigner Crystal on Helium in Quasi-One-Dimensional Geometry
(2015-05-01)
Ikegami, Hiroki
;
Akimoto, Hikota
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Kono, Kimitoshi
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物理研究所
;
Institute of Physics
We discuss melting of a Wigner crystal formed on a free surface of superfluid He, in quasi-one-dimensional (Q1D) channels of width between 5 and 15 m. We reexamine our previous transport data (Ikegami et al. in Phys Rev B 82:201104(R), 2010), in particular, by estimating the number of electrons across the channel in a more accurate way with the aid of numerical calculations of distributions of the electrons in the channels. The results of reexamination indicate more convincingly that the melting of the Wigner crystal in the Q1D geometry is understood by the finite size effect on the Kosterlitz-Thouless-Halperin-Nelson-Young melting process. We also present technical details of the transport measurements of the electrons in a Q1D geometry, including a fabrication method of devices used for the transport measurements, numerical simulations of response of the devices, and a procedure for analyzing transport data.
Observation of Intrinsic Magnus Force and Direct Detection of Chirality in Superfluid He-3-A
(2015-04-15)
Ikegami, Hiroki
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Tsutsumi, Yasumasa
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Kono, Kimitoshi
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物理研究所
;
Institute of Physics
We report details of the observation of the intrinsic Magnus (IM) force acting on negative and positive ions trapped just below a free surface of the A phase of superfluid He-3 (He-3-A). From the transport measurements of the ions along the surface, we found that the IM force acts on both the negative and positive ions. We also demonstrate that the transport measurements could distinguish whether the surface is composed of a chiral monodomain or multiple chiral domains. For multiple chiral domains, the current of the ions was found to be irreproducible and unstable, which was reasonably explained by the formation of the chiral domain structure and the dynamics of the chiral domain walls. For chiral monodomains, the appearance ratio of chirality emerging upon cooling through the superfluid transition temperature was found to depend on the direction of the external magnetic field, which implies the existence of an unknown coupling between the chirality and the magnetic field.
Reentrant Melting of a Classical Quasi-One-Dimensional Wigner Crystal on the Surface of Liquid Helium
(2013-12-01)
Rees, David G.
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Ikegami, Hiroki
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Kono, Kimitoshi
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物理研究所
;
Institute of Physics
We present transport measurements of electrons on the surface of liquid helium confined to a microscopic channel, the effective width of which can be controlled electrostatically. Above 1 K the electron system is liquid-like and the conductance varies smoothly with the channel width. At lower temperatures the system forms a classical quasi-one-dimensional Wigner crystal ( WC). Close to the WC melting temperature, the current oscillates as the channel width is varied, due to reentrant melting as recently reported [H. Ikegami, H. Akimoto, D. G. Rees, and K. Kono: Phys. Rev. Lett. 109 ( 2012) 236802]. In the WC regime we observe Bragg-Cherenkov ripplon scattering, a signature of strong spatial electron order, for both the widely open channel and the single electron chain.
Review: Observation of Majorana Bound States at a Free Surface of <mml:msup>3</mml:msup>He-B
(2019-05-01)
Ikegami, Hiroki
;
Kono, Kimitoshi
;
電子物理學系
;
Department of Electrophysics
The p-wave superfluid 3He is a textbook example of topological superfluids. Among its multiple superfluid phases, the B phase (3He-B) is known as a topological state protected by time-reversal symmetry. One of the important topological features of 3He-B is the formation of bound states at its surface. Notably, such surface Andreev bound states are predicted to be Majorana fermions, i.e., their antiparticles are identical to their particles. Because of the well-elucidated bulk properties of the superfluid 3He owing to its cleanliness, 3He-B provides an ideal platform to pursue Majorana fermions in condensed matter systems. In this article, we review recent investigations of surface Andreev bound states by the mobility of ions trapped below a free surface of 3He-B. The free surface is an ideal surface providing a specular boundary condition; the surface Andreev bound states formed there are expected to be Majorana fermions with a well-defined energy spectrum. We show that the temperature and depth dependences of the experimentally obtained mobility of negative ions (Ikegami et al. in J Phys Soc Jpn 82:124607, 2013) are quantitatively reproduced by a theoretical study that includes scattering of the surface Andreev bound states (Tsutsumi in Phys Rev Lett 118:145301, 2017). This quantitative agreement unambiguously demonstrates the experimental detection of surface Andreev bound states. We also discuss the future prospects of the Majorana physics in He-3-B.