Thermodynamic behavior of the XXZ Heisenberg s=1/2 chain around the factorizing magnetic field

TL;DR

This paper studies the thermodynamic and entanglement properties of the XXZ Heisenberg spin-1/2 chain near the factorizing magnetic field, revealing a double peak in specific heat and phase transitions using spin wave theory and Lanczos data.

Contribution

It introduces a detailed analysis of the thermodynamics and entanglement behavior around the factorizing field, combining spin wave theory with numerical Lanczos calculations.

Findings

Entanglement is exactly lost at the factorizing field h_f.

A double peak in specific heat indicates two energy scales.

Ground state becomes a product state at h_f, enabling spin wave analysis.

Abstract

We have investigated the zero and finite temperature behaviors of the anisotropic antiferromagnetic Heisenberg XXZ spin-1/2 chain in the presence of a transverse magnetic field (h). The attention is concentrated on an interval of magnetic field between the factorizing field (h_f) and the critical one (h_c). The model presents a spin-flop phase for 0<h<h_f with an energy scale which is defined by the long range antiferromagnetic order while it undergoes an entanglement phase transition at h=h_f. The entanglement estimators clearly show that the entanglement is lost exactly at h=h_f which justifies different quantum correlations on both sides of the factorizing field. As a consequence of zero entanglement (at h=h_f) the ground state is known exactly as a product of single particle states which is the starting point for initiating a spin wave theory. The linear spin wave theory is implemented to obtain the specific heat and thermal entanglement of the model in the interested region. A double peak structure is found in the specific heat around h=h_f which manifests the existence of two energy scales in the system as a result of two competing orders before the critical point. These results are confirmed by the low temperature Lanczos data which we have computed.