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Quantum and classical criticality in a dimerized quantum antiferromagnet

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Merchant P., Normand B., Krämer K. W., Boehm M., McMorrow D. F., Rüegg Ch.,
Project Dimensional and Anisotropy Control of Model Quantum Magnets
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Original article (peer-reviewed)

Journal Nature Physics
Volume (Issue) 10(5)
Page(s) 373 - 379
Title of proceedings Nature Physics
DOI 10.1038/nphys2902

Open Access

Type of Open Access Repository (Green Open Access)


A quantum critical point (QCP) is a singularity in the phase diagram arising because of quantum mechanical fluctuations. The exotic properties of some of the most enigmatic physical systems, including unconventional metals and superconductors, quantum magnets and ultracold atomic condensates, have been related to the importance of critical quantum and thermal fluctuations near such a point. However, direct and continuous control of these fluctuations has been dicult to realize, and complete thermodynamic and spectroscopic information is required to disentangle the eects of quantum and classical physics around a QCP. Here we achieve this control in a high-pressure, high-resolution neutron scattering experiment on the quantum dimer material TlCuCl3. By measuring the magnetic excitation spectrum across the entire quantum critical phase diagram, we illustrate the similarities between quantum and thermal melting of magnetic order. We prove the critical nature of the unconventional longitudinal (Higgs) mode of the ordered phase by damping it thermally.We demonstrate the development of two types of criticality, quantum and classical, and use their static and dynamic scaling properties to conclude that quantum and thermal fluctuations can behave largely independently near a QCP.