Insights into Magnetic Properties of a Mixed Spin-Electron Model on Decorated Planar Lattices Composed of Half-filled Trigonal Bipyramids

TL;DR

This paper exactly solves a mixed spin-electron model on decorated planar lattices with trigonal bipyramids, revealing two long-range ordered phases and analyzing their thermal stability and degeneracy.

Contribution

It introduces an exact solution for a complex spin-electron model on decorated lattices, highlighting the coexistence of classical and quantum phases with distinct degeneracies.

Findings

Classical phase exhibits perfect ferromagnetic order.

Quantum phase has macroscopic degeneracy due to chiral electron states.

Classical arrangement is thermally more stable than quantum for certain parameters.

Abstract

A mixed spin-electron model on decorated planar lattices formed by corner-sharing trigonal bipyramids is exactly solved by imposing three mobile electrons per triangular cluster of each bipyramid by means of a generalized decoration-iteration mapping transformation. It is shown that the ground state of the model involves two spontaneously long-range ordered phases, namely, the classical phase with a perfect ferromagnetic arrangement of all particles and the macroscopically degenerate quantum one. The macroscopic degeneracy of the quantum phase lies in chiral degrees of freedom of the mobile electrons. Finite-temperature phase diagrams as well as temperature variations of the spontaneous magnetization, entropy, and specific heat clearly prove that the classical spin-electron arrangement is thermally almost twice more stable than the quantum one for some combinations of the model's parameters.