Stick-Slip Motion of the Wigner Solid on Liquid Helium
David G. Rees1,2*, Niyaz R. Beysengulov2,3, Juhn-Jong Lin1,2,4, Kimitoshi Kono1,2,3
1Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan
2CEMS, RIKEN, Wako-shi, Japan
3Institute of Physics, Kazan Federal University, Kazan, Russian Federation
4Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
* presenting author:David Rees,
Surface-state electrons (SSEs) on liquid helium substrates form a model 2D Coulomb system, the ground state of which remains the clearest example of the classical Wigner solid (WS)[1]. At rest, the WS is ‘dressed’ by a cloud of quantised capillary waves (ripplons), the Bragg scattering of which from the electron lattice gives rise to a commensurate deformation of the He surface known as the dimple lattice (DL)[2]. Under a sufficiently high driving force, the electron lattice decouples from the DL and ‘slides’ along the helium surface with high velocity[3]. Such dynamics are analogous to the detrapping of polaron states in which electrons are dressed by a cloud of virtual phonons[4]. The study of the WS-DL decoupling therefore provides insights into polaron dynamics as well as a unique oppourtunity to investigate collective electron motion on a perfectly clean substrate.
Here we present the first time-resolved measurements of the WS-DL decoupling. We measure the flow of SSEs along a helium substrate confined in a microchannel 100 μm long and 7.5 μm wide. The electron density, and so the number of electron rows in the quasi-1D WS, is controlled electrostatically using gate electrodes. We ramp the driving potential over several tens of microseconds, and record the current flowing in the microchannel. The electron system first exhibits a dynamical pinning at a particular electron velocity due to resonant Bragg-Cherenkov ripplon scattering[5]. Then, as the driving force builds, the WS slides from the DL and the current increases sharply, before relaxing as the driving force decreases. We find that this stick-slip process can occur repeatedly as the driving potential is ramped, giving rise to spontaneous narrow-band current noise. Such behavior can be compared with similar observations for degenerate electron systems in the WS regime[6]. We demonstrate a quantitative understanding of the nonlinear electron motion and that our microchannel device allows sensitive control of the current oscillation frequency. SSEs are therefore a promising system for the study of polaron-type decoupling dynamics and stick-slip friction at the nanoscale[7].

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Keywords: Electrons on helium, Wigner solid, Stick-slip friction, Microchannel, Bragg-Cherenkov scattering