Vigorous thermal excitations in a double-tetrahedral chain of localized Ising spins and mobile electrons mimic a temperature-driven first-order phase transition

TL;DR

This paper exactly solves a hybrid spin-electron chain model revealing how thermal excitations can mimic a temperature-driven first-order phase transition, with significant implications for thermodynamic behavior and degeneracy effects.

Contribution

It introduces an exactly solvable model of a spin-electron chain demonstrating thermal excitation-induced phase transition-like behavior and degeneracy effects.

Findings

Thermal excitations mimic a first-order phase transition.

Massive degeneracy causes a low-temperature specific heat peak.

Abrupt changes in entropy and magnetizations observed.

Abstract

A hybrid spin-electron system defined on one-dimensional double-tetrahedral chain, in which the localized Ising spin regularly alternates with two mobile electrons delocalized over a triangular plaquette, is exactly solved with the help of generalized decoration-iteration transformation. It is shown that a macroscopic degeneracy of ferromagnetic and ferrimagnetic ground states arising from chiral degrees of freedom of the mobile electrons cannot be lifted by a magnetic field in contrast to a macroscopic degeneracy of the frustrated ground state, which appears owing to a kinetically-driven frustration of the localized Ising spins. An anomalous behavior of all basic thermodynamic quantities can be observed on account of massive thermal excitations, which mimic a temperature-driven first-order phase transition from the non-degenerate frustrated state to the highly degenerate ferrimagnetic state at non-zero magnetic fields. A substantial difference in the respective degeneracies is responsible for an immense low-temperature peak of the specific heat and very abrupt (almost discontinuous) thermal variations of the entropy and sublattice magnetizations.