Sliding of Electron Crystal of Finite Size on the Surface of Superfluid He-4 Confined in a Microchannel

TL;DR

This study investigates how the size of a finite electron crystal on superfluid helium affects its decoupling from surface deformations, revealing size-dependent thresholds explained by ripplon radiative loss.

Contribution

It introduces an analytical model explaining the size-dependent decoupling threshold of electron crystals on helium surfaces, emphasizing ripplon radiative loss effects.

Findings

Decoupling threshold decreases for crystals shorter than 25 micrometers.

Surface deformations weaken due to ripplon radiative loss in finite-sized crystals.

Analytical model successfully explains size-dependent decoupling behavior.

Abstract

We present a new study of the nonlinear transport of a two-dimensional electron crystal on the surface of liquid helium confined in a 10 micrometer-wide channel in which the effective length of the crystal can be varied from 10 to 215 micrometers. At low driving voltages, the moving electron crystal is strongly coupled to deformation of the liquid surface arising from resonant excitation of surface capillary waves, ripplons, while at higher driving voltages the crystal decouples from the deformation. We find strong dependence of the decoupling threshold of the driving electric field acting on the electrons, on the size of the crystal. In particular, the threshold electric field significantly decreases when the length of the crystal becomes shorter than 25 micrometers. We explain this effect as arising from weakening of surface deformations due to radiative loss of resonantly-excited ripplons from an electron crystal of finite size, and we account for the observed effect using an instructive analytical model.