Dual thermal pseudocritical features in a spin-1/2 Ising chain with twin-diamond geometry

TL;DR

This paper analyzes a coupled twin-diamond Ising chain, revealing dual pseudocritical features and phase behavior driven by frustration, using an exact solution approach that highlights complex thermodynamic phenomena in one dimension.

Contribution

It introduces an exactly solvable model of a coupled twin-diamond Ising chain exhibiting dual thermal pseudocritical features due to frustration and degeneracy.

Findings

Identification of five distinct phases including frustrated sectors

Observation of entropy plateaus and pseudotransition signatures

Exact thermodynamic description via transfer-matrix formulation

Abstract

We study the coupled twin-diamond chain, a decorated one-dimensional Ising model motivated by the magnetic structure of $\mathrm{Cu}_{2}(\mathrm{TeO}_{3})_{2}\mathrm{Br}_{2}$. By applying an exact mapping to an effective Ising chain, we obtain the full thermodynamic description of the system through a compact transfer-matrix formulation. The ground-state analysis reveals five distinct phases, including two frustrated sectors with extensive degeneracy. These frustrated regions give rise to characteristic entropy plateaus and separate the ordered phases in the zero-temperature diagram. At low temperatures the model exhibits peculiar sharp yet continuous variations of entropy, magnetization, and response functions, reflecting clear signatures of pseudotransition behavior. The coupled twin-diamond chain thus provides an exactly solvable setting in which competing local configurations and internal frustration lead to pronounced dual pseudocritical features in one dimension.