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Quantum criticality in an organic magnet.
M B Stone1, C Broholm, D H Reich
1Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennennesse 37831, USA.
Physical Review Letters
|August 16, 2006
Summary
This study reveals the field-temperature phase diagram of a frustrated bilayer magnet, identifying two quantum critical points. The material exhibits an ordered phase described as a magnon Bose-Einstein condensate (BEC).
Area of Science:
- Condensed Matter Physics
- Quantum Magnetism
- Materials Science
Background:
- Piperazinium hexachlorodicuprate features S=1/2 sites with exchange interactions, leading to a frustrated bilayer magnet.
- The material exhibits a singlet ground state, characteristic of complex magnetic interactions.
Purpose of the Study:
- To determine the field-temperature phase diagram of piperazinium hexachlorodicuprate.
- To investigate the nature of magnetic ordering and quantum criticality in this frustrated magnet.
Main Methods:
- High field magnetization measurements.
- Neutron scattering experiments.
Main Results:
- Two quantum critical points were identified at Hc1=7.5 T and Hc2=37 T.
- A three-dimensional antiferromagnetically ordered phase, described as a magnon Bose-Einstein condensate (BEC), was observed between Hc1 and Hc2.
- The BEC phase is embedded in a quantum critical regime with short-range correlations.
- A low-temperature anomaly in the BEC phase boundary suggests the importance of additional low-energy features near Hc1.
Conclusions:
- The study elucidates the complex magnetic phase diagram of a frustrated bilayer magnet.
- The identification of a magnon Bose-Einstein condensate phase highlights novel quantum phenomena in this material.
- Further investigation into low-energy features near Hc1 is warranted.