Thermal first-order phase transitions, Ising critical points, and reentrance in the Ising-Heisenberg model on the diamond-decorated square lattice in a magnetic field

TL;DR

This paper investigates thermal phase transitions in an Ising-Heisenberg model on a decorated lattice, revealing exact first-order transitions, Ising critical points, and reentrant behavior through a combination of analytical mapping and Monte Carlo simulations.

Contribution

It introduces an exact mapping of the quantum model to an effective classical Ising model, enabling precise analysis of phase transitions and reentrance phenomena.

Findings

Exact surface of first-order phase transitions identified.

Line of Ising critical points determined.

Reentrant phase transitions observed in narrow parameter regimes.

Abstract

The thermal phase transitions of a spin-1/2 Ising-Heisenberg model on the diamond-decorated square lattice in a magnetic field are investigated using a decoration-iteration transformation and classical Monte Carlo simulations. A generalized decoration-iteration transformation maps this model exactly onto an effective classical Ising model on the square lattice with temperature-dependent effective nearest-neighbor interactions and magnetic field strength. The effective field vanishes along a ground-state phase boundary of the original model, separating a ferrimagnetic and a quantum monomer-dimer phase. At finite temperatures this phase boundary gives rise to an exactly solvable surface of discontinuous (first-order) phase transitions, which terminates in a line of Ising critical points. The existence of discontinuous reentrant phase transitions within a narrow parameter regime is reported and explained in terms of the low-energy excitations from both phases. These exact results, obtained from the mapping to the zero-field effective Ising model are corroborated by classical Monte Carlo simulations of the effective model.