Collective Modes in Two Dimensional Binary Yukawa Systems

TL;DR

This paper investigates the collective excitations in two-dimensional binary Yukawa systems using theoretical models and simulations, revealing detailed mode structures in both liquid and solid phases.

Contribution

It introduces a combined theoretical and simulation approach to analyze collective modes in binary Yukawa systems across different phases.

Findings

Identification of longitudinal and transverse acoustic and optic modes.

Discontinuous evolution of the longitudinal acoustic mode from weak to strong coupling.

Relation of high frequency optic modes to Einstein frequencies.

Abstract

We analyze via theoretical approaches and molecular dynamics simulations the collective mode structure of strongly coupled two-dimensional binary Yukawa systems, for selected density, mass and charge ratios, both in the liquid and crystalline solid phases. Theoretically, the liquid phase is described through the Quasi-Localized Charge Approximation (QLCA) approach, while in the crystalline phase we study the centered honeycomb and the staggered rectangular crystal structures through the standard harmonic phonon approximation. We identify "longitudinal" and "transverse" acoustic and optic modes and find that the longitudinal acoustic mode evolves from its weakly coupled counterpart in a discontinuous non-perturbative fashion. The low frequency acoustic excitations are governed by the oscillation frequency of the average atom, while the high frequency optic excitation frequencies are related to the Einstein frequencies of the systems.