Mixed Heisenberg Chains. II. Thermodynamics

TL;DR

This paper studies the thermodynamic properties of alternating Heisenberg spin chains, revealing features like double peaks in specific heat due to quantum phase transitions, by decomposing the chains into finite fragments and analyzing their statistical ensemble.

Contribution

It introduces a method to analyze thermodynamics of alternating Heisenberg chains by exploiting a hidden Ising symmetry and fragment decomposition, linking quantum phase transitions to observable thermodynamic features.

Findings

Specific heat shows double peaks at low temperatures.

Thermodynamic properties are linked to zero-temperature quantum phase transitions.

Chains can be effectively analyzed by separating finite fragments and ensemble averaging.

Abstract

We consider thermodynamic properties, e.g. specific heat, magnetic susceptibility, of alternating Heisenberg spin chains. Due to a hidden Ising symmetry these chains can be decomposed into a set of finite chain fragments. The problem of finding the thermodynamic quantities is effectively separated into two parts. First we deal with finite objects, secondly we can incorporate the fragments into a statistical ensemble. As functions of the coupling constants, the models exhibit special features in the thermodynamic quantities, e.g. the specific heat displays double peaks at low enough temperatures. These features stem from first order quantum phase transitions at zero temperature, which have been investigated in the first part of this work.