Quantum criticality in the spin-${1}/{2}$ Heisenberg chain system copper pyrazine dinitrate

TL;DR

This study investigates the quantum critical behavior of copper pyrazine dinitrate, a spin-1/2 chain system, through thermodynamic measurements that align with theoretical predictions, illustrating fundamental principles of quantum critical thermodynamics.

Contribution

The paper provides a comprehensive experimental validation of quantum criticality in a real material, matching thermodynamic data with exact theoretical models near the critical point.

Findings

Thermodynamic measurements agree with Bethe-Ansatz predictions.

Quantum critical scaling behavior observed near the critical field.

Divergence of magnetocaloric effect and Grüneisen parameters at criticality.

Abstract

The magnetic insulator copper pyrazine dinitrate comprises antiferromagnetic spin-1/2 chains that are well described by the exactly solvable one-dimensional Heisenberg model, providing a unique opportunity for a quantitative comparison between theory and experiment. Here, we investigate its thermodynamic properties with a particular focus on the field-induced quantum phase transition. Thermal expansion, magnetostriction, specific heat, magnetization and magnetocaloric measurements are found to be in excellent agreement with predictions from exact Bethe-Ansatz results as well as from effective field theory. Close to the critical field, thermodynamics obeys the expected quantum critical scaling behavior, and, in particular, the magnetocaloric effect and the Gr\"uneisen parameters diverge in a characteristic manner. Apart from realizing a paradigm of quantum criticality, our study instructively illustrates fundamental principles of quantum critical thermodynamics.