RQC Seminar

35th RQC Seminar

  • Speaker

    Dr. Vyacheslav Misko
    (Department of Chemical Engineering, Vrije Universiteit Brussel, Belgium)

  • Date

    16:00-17:00 (JST), March 30, 2023 (Thursday)

  • Venue

    Hybrid (Zoom / Wako Welfare and Conf. 2F Large Meeting Room RIKEN Wako branch)

  • Title

    Finite-temperature Wigner solid and other phases of ripplonic polarons on a helium film

  • Inquiries

    rqc_info[at]ml.riken.jp

Abstract
Electrons on liquid helium can form different phases depending on density and temperature. The electron-ripplon coupling strength influences the phase diagram through the formation of so-called “ripplonic polarons”1,2 that influences the electron localization which, in turn, shifts the transition between the Wigner solid and liquid phases. We use an all-coupling, finite-temperature variational method3 to study the formation of a ripplopolaron Wigner solid on a liquid helium film for different regimes of the electron-ripplon coupling strength. In addition to the three known phases of the ripplopolaron system (electron Wigner solid, polaron Wigner solid, and electron fluid), we define and identify a fourth distinct phase, the ripplopolaron liquid. We analyze the transitions between these four phases, including quantum melting at low temperatures, and calculate the corresponding phase diagrams. A reentrant melting of the electron solid is revealed as a function of temperature. The calculated regions of existence of the Wigner solid are in agreement with recent experimental observations. In very narrow channels, a quasi-one-dimensional (quasi-1D) Wigner crystal can be formed by just a few rows of electrons and, ultimately, one row in the “quantum wire” regime4 resulting in unusual transport phenomena such as, e.g., oscillations in the electron conductance.4 Our recent numerical studies,5 using molecular-dynamics simulations of Langevin equations of motion of interacting electrons on surface of liquid 4He, revealed a significant difference in the electron dynamics for long and short constrictions. The pronounced current oscillations found for a short constriction were shown to be suppressed for longer constrictions, in agreement with the experimental observations.4 We also briefly discuss a related system of floating “microscopic ions” recently realized in experiment.6

[1] M. W. Cole, Rev. Mod. Phys. 46, 451 (1974).
[2] Two-Dimensional Electron Systems on Helium and other Cryogenic Substrates
(ed. E. Y. Andrei, Kluwer Acad. Publ, Dordrecht, The Netherlands, 1997). [3] S. N. Klimin, J. Tempere, V. R. Misko ＆ M. Wouters, Eur. Phys. J. B 89, 172 (2016).
[4] D. G. Rees, H. Totsuji ＆ K. Kono, Phys. Rev. Lett. 108, 176801 (2012).
[5] A. A. Vasylenko ＆ V. R. Misko, Biophys. Rev. Lett. 9, 349 (2014); Eur. Phys. J. B 88, 105 (2015).
[6] T. Huang, V. Misko, A. Caspari, A. Synytska, B. Ibarlucea, F. Nori, J. Fassbender, G. Cuniberti,
D. Makarov ＆ L. Baraban, Commun. Mater. 3, 1, 60 (2022).

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