Phase transitions in a system of hard $Y$-shaped particles on the triangular lattice

TL;DR

This study investigates phase transitions in a system of Y-shaped particles on a triangular lattice, revealing two entropy-driven first-order transitions from disordered to ordered phases as density increases.

Contribution

It introduces a detailed analysis of phase behavior in Y-shaped particles, including the discovery of two distinct entropy-driven phase transitions and their characteristics.

Findings

Two entropy-driven phase transitions identified

Disordered to sublattice phase transition at intermediate densities

Sublattice to columnar phase transition at high densities

Abstract

We study the different phases and the phase transitions in a system of $Y$-shaped particles, examples of which include Immunoglobulin-G and trinaphthylene molecules, on a triangular lattice interacting exclusively through excluded volume interactions. Each particle consists of a central site and three of its six nearest neighbours chosen alternately, such that there are two types of particles which are mirror images of each other. We study the equilibrium properties of the system using grand canonical Monte Carlo simulations that implements an algorithm with cluster moves that is able to equilibrate the system at densities close to full packing. We show that, with increasing density, the system undergoes two entropy-driven phase transitions with two broken-symmetry phases. At low densities, the system is in a disordered phase. As intermediate phases, there is a solid-like sublattice phase in which one type of particle is preferred over the other and the particles preferentially occupy one of four sublattices, thus breaking both particle-symmetry as well as translational invariance. At even higher densities, the phase is a columnar phase, where the particle-symmetry is restored, and the particles preferentially occupy even or odd rows along one of the three directions. This phase has translational order in only one direction, and breaks rotational invariance. From finite size scaling, we demonstrate that both the transitions are first order in nature. We also show that the simpler system with only one type of particles undergoes a single discontinuous phase transition from a disordered phase to a solid-like sublattice phase with increasing density of particles.