Specific Heat Study of an S=1/2 Alternating Heisenberg Chain System F_5PNN Under Magnetic Field

TL;DR

This study investigates the specific heat of an S=1/2 alternating Heisenberg chain compound under magnetic fields, revealing behaviors consistent with theoretical models and indicating low-energy excitations in a Tomonaga-Luttinger liquid.

Contribution

First experimental measurement of specific heat in an S=1/2 alternating Heisenberg chain under high magnetic fields, linking results to theoretical models and low-energy excitations.

Findings

Behavior changes with magnetic field, especially above H_C2.

Qualitative agreement with two-leg ladder theoretical calculations.

Evidence of low-energy excitations in the Tomonaga-Luttinger liquid regime.

Abstract

We have measured the specific heat of an S=1/2 antiferromagnetic alternating Heisenberg chain pentafulorophenyl nitronyl nitroxide under magnetic fields up to H>H_C2. This compound has the field-induced magnetic ordered (FIMO) phase between H_C1 and H_C2. Characteristic behaviors are observed depending on the magnetic field up to above H_C2 outside of the H-T boundary for the FIMO. Temperature and field dependence of the specific heat are qualitatively in good agreement with the theoretical calculation on an S=1/2 two-leg ladder. [Wang et al. Phys. Rev. Lett 84 5399 (2000)] This agreement suggests that the observed behaviors are related with the low-energy excitation in the Tomonaga-Luttinger liquid.