Self-diffusion in a spatially modulated system of electrons on helium

TL;DR

This study uses molecular dynamics simulations to explore how electrons on helium behave under different conditions, revealing how diffusion and phase transitions depend on temperature and external potentials.

Contribution

It demonstrates the impact of a periodic potential on electron diffusion and phase transition behavior, highlighting the stability of Wigner crystals in such environments.

Findings

Self-diffusion coefficient decreases superlinearly with temperature.

Discontinuous freezing in free electron systems; smooth freezing in periodic potential.

Presence of incommensurability solitons in the solid phase.

Abstract

We present results of molecular dynamics simulations of the electron system on the surface of liquid helium. The simulations are done for 1600 electrons with periodic boundary conditions. Electron scattering by capillary waves and phonons in helium is explicitly taken into account. We find that the self-diffusion coefficient superlinearly decreases with the decreasing temperature. In the free electron system it turns to zero essentially discontinuously, which we associate with the liquid to solid transition. In contrast, when the system is placed in the fully commensurate one-dimensional potential the freezing of the diffusion occurs smoothly. We relate this change to the fact that, as we show, a Wigner crystal in such a potential is stable, in contrast to systems with a short-range inter-particle coupling. We find that the freezing temperature nonmonotonically depends on the commensurability parameter. We also find incommensurability solitons in the solid phase. The results reveal peculiar features of the dynamics of a strongly correlated system with long-range coupling placed into a periodic potential.