Abstract
The heat transport of the spin-gapped material , a candidate quantum magnet with Bose-Einstein condensation (BEC), is studied at ultralow temperatures and in high magnetic fields. Due to the presence of the spin gap, the zero-field thermal conductivity is purely phononic and shows a ballistic behavior at K. When the gap is closed by magnetic field at , where a long-range antiferromanetic (AF) order of moments is developed, the magnons contribute significantly to heat transport and exhibit a ballistic behavior at mK. In addition, the low- isotherms show sharp peaks at , which indicates a gap reopening in the AF state and demonstrates limited applicability of the BEC model to .
- Received 1 January 2015
- Revised 4 April 2015
DOI:https://doi.org/10.1103/PhysRevB.91.134420
©2015 American Physical Society