Phase diagram and melting scenarios of two-dimensional Hertzian spheres

TL;DR

This study uses computer simulations to explore the phase diagram and melting behaviors of two-dimensional Hertzian spheres, revealing multiple ordered phases, diverse melting scenarios, and the potential for a tricritical point.

Contribution

It provides the first detailed analysis of melting scenarios and phase behavior of 2D Hertzian spheres, including the discovery of a tricritical point and various melting pathways.

Findings

Identification of multiple ordered phases including dodecagonal quasicrystals

Observation of different melting scenarios, including BKTHNY and first-order transitions

Evidence for a tricritical point on the melting line

Abstract

We present computer simulations of a system of purely repulsive soft colloidal particles interacting via the Hertz potential and constrained to a two-dimensional plane. This potential describes the elastic interaction of weakly deformable bodies and can be a reliable model for qualitative description of behavior of soft macromolecules, like globular micelles and star polymers. We find a large number of ordered phases, including the dodecagonal quasicrystal, and analyze the melting scenarios of low density triangle and square phases. It is interesting that depending on the position on the phase diagram the system can melt both through the first order transition and in accordance with the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young (BKTHNY) scenario (two continuous transitions with the intermediate hexatic phase) and also in accordance with recently proposed two-stage melting with the first order hexatic-isotropic liquid transition and continuous solid-hexatic transition. We also demonstrate the possibility of the tricritical point on the melting line.