Melting scenarios of two-dimensional Hertzian spheres with a single triangular lattice

TL;DR

This study uses molecular dynamics to explore the phase diagram and melting behaviors of two-dimensional Hertzian spheres, revealing multiple re-entrant melting and various melting scenarios including BKTHNY and two-stage melting.

Contribution

It provides the first detailed analysis of melting scenarios of 2D Hertzian spheres with exponent 7/2, highlighting multiple re-entrant melting and different transition pathways.

Findings

Multiple re-entrant melting observed across a wide density range.

Melting occurs via both two-stage and BKTHNY scenarios depending on conditions.

Heat capacity peaks correspond to solid-hexatic transition despite two-stage melting.

Abstract

We present a molecular dynamics simulation study of the phase diagram and melting scenarios of two-dimensional Hertzian spheres with exponent 7/2. We have found multiple re-entrant melting of a single crystal with a triangular lattice in a wide range of densities from 0.5 to 10.0. Depending on the position on the phase diagram, the triangular crystal has been shown to melt through both two-stage melting with a first-order hexatic - isotropic liquid transition and a continuous solid - hexatic transition as well as in accordance with the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young (BKTHNY) scenario (two continuous transitions with an intermediate hexatic phase). We studied the behavior of heat capacity and have shown that despite two-stage melting, the heat capacity has one peak which seems to correspond to a solid-hexatic transition.