Buckling of 2D Plasma Crystals with Non-reciprocal Interactions

TL;DR

This paper investigates how non-reciprocal interactions due to plasma wakes influence the buckling behavior of 2D plasma crystals, revealing transitions to bilayer structures not seen in reciprocal systems.

Contribution

It introduces a detailed analysis of buckling in 2D plasma crystals considering non-reciprocal wake interactions, predicting novel bilayer phase transitions.

Findings

Monolayer hexagonal crystals transition to bilayer hexagonal structures.

Further transition to bilayer square structures occurs with decreased confinement.

Molecular dynamics simulations confirm theoretical predictions for experimental parameters.

Abstract

Laboratory realizations of 2D plasma crystals typically involve monodisperse microparticles confined into horizontal monolayers in radio-frequency (rf) plasma sheaths. This gives rise to the so-called plasma wakes beneath the microparticles. The presence of wakes renders the interactions in such systems non-reciprocal, a fact that can lead to a quite different behaviour from the one expected for their reciprocal counterparts. Here we examine the buckling of a hexagonal 2D plasma crystal, occurring as the confinement strength is decreased, taking explicitly into account the non-reciprocity of the system via a well-established point-particle wake model. We observe that for a finite wake charge, the monolayer hexagonal crystal undergoes a transition first to a bilayer hexagonal structure, unrealisable in harmonically confined reciprocal Yukawa systems, and subsequently to a bilayer square structure. Our theoretical results are confirmed by molecular dynamics simulations for experimentally relevant parameters, indicating the potential of their observation in state-of-the-art experiments with 2D complex plasmas.