Electrons on Helium Surface: Commensurate-Incommensurate Transitions

Electrons on the surface of liquid helium are strongly correlated. This system enables studying the interplay between strong correlations and periodic spatial modulation in a free from defects environment. The modulation can be electrostatic or magnetic, coming from structures submerged into helium at a micron depth, which is the typical interelectron distance. Its strength and spatial structure can be controlled, and the temperature can be varied across the liquid to Wigner crystal transition. We have performed molecular dynamics simulations to study the structure and the ac and dc transport of the electron system in a one-dimensional periodic electrostatic potential. We show that the potential strongly affects the temperature of the electron freezing and can significantly smear the freezing transition. Because the Coulomb interaction is isotropic, many-electron “accommodation” to the external potential can display features different from those in solid-on-solid structures. We find that the electron transport sensitively depends on the emerging electron structure. We discuss how a periodic structure can be revealed using resonant ac conductivity and the spectrum of the inter-subband microwave absorption.