Quantum criticality and universal scaling of a quantum antiferromagnet

TL;DR

This study investigates the universal quantum critical behavior of the antiferromagnetic material KCuF3, demonstrating the validity of Luttinger liquid theory over a wide parameter range and identifying deviations at certain energies and temperatures.

Contribution

It provides comprehensive experimental evidence of quantum criticality and universal scaling in a real material near a quantum critical point, validating theoretical predictions.

Findings

Luttinger liquid description applies over a broad range of parameters

Deviations from LL behavior are observed at high and low energies and temperatures

Neutron scattering data confirms universal features of quantum criticality

Abstract

Quantum effects dominate the behaviour of many diverse materials. Of particular current interest are those systems in the vicinity of a quantum critical point (QCP). Their physical properties are predicted to reflect those of the nearby QCP with universal features independent of the microscopic details. The prototypical QCP is the Luttinger liquid (LL) which is of relevance to many quasi-one-dimensional materials. The magnetic material KCuF3 realizes an array of weakly-coupled spin chains (or LLs) and thus lies close to but not exactly at the Luttinger liquid quantum critical point. By using inelastic neutron scattering we have collected a complete data set of the magnetic correlations of KCuF3 as a function of momentum, energy, and temperature. The LL description is found to be valid over an extensive range of these parameters, and departures from this behaviour at high and low energies and temperatures have been identified and explained.