On the orientational ordering of long rods on a lattice

TL;DR

This paper investigates phase transitions in a lattice model of long rods, revealing two distinct transitions: from disordered to nematic and back to disordered, as density varies for rods of length seven or more.

Contribution

It demonstrates the existence of two phase transitions in a lattice system of long rods, including a reentrant transition, which was not previously characterized.

Findings

Two phase transitions occur for rods with length >= 7.

Reentrant transition from nematic to disordered phase.

Critical densities for phase transitions identified.

Abstract

We argue that a system of straight rigid rods of length k on square lattice with only hard-core interactions shows two phase transitions as a function of density, rho, for k >= 7. The system undergoes a phase transition from the low-density disordered phase to a nematic phase as rho is increased from 0, at rho = rho_c1, and then again undergoes a reentrant phase transition from the nematic phase to a disordered phase at rho = rho_c2 < 1.