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

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 pseudo-transition behavior. The coupled twin-diamond chain thus provides an exactly solvable setting in which competing local configurations and internal frustration lead to pronounced dual pseudo-critical features in one dimension.