Still life in a classic Blume-Capel model: pseudo-transitions in a spin-1 diamond chain

Abstract

We exactly investigate the ground-state, magnetic, and thermodynamic properties of a spin-1 Blume-Capel diamond chain in a magnetic field by means of the transfer-matrix method. After establishing the complete ground-state phase diagram and characterizing each ground-state spin configuration, we examine the finite-temperature behavior in the vicinity of selected phase boundaries and triple points. It is demonstrated that an extremely small energy gap between a nondegenerate ground state and competing macroscopically degenerate low-lying excited states gives rise to entropically-driven pseudo-transitions. These pseudo-transitions manifest themselves through abrupt but continuous changes in the magnetization and entropy resembling discontinuous jumps, while the magnetic susceptibility and specific heat exhibit exceptionally sharp yet finite peaks resembling divergences. Our results provide the exact evidence that pseudo-transitions can also emerge in the classical spin-1 Blume-Capel model and thereby extend the class of one-dimensional spin systems known to display pseudo-transitions.