Novel Strongly Spin-Orbit Coupled Quantum Dimer Magnet: Yb2Si2 O 7

The quantum dimer magnet (QDM) is the canonical example of quantum magnetism. The QDM state consists of entangled nearest-neighbor spin dimers and often exhibits a field-induced triplon Bose-Einstein condensate (BEC) phase. We report on a new QDM in the strongly spin-orbit coupled, distorted honeyco...

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Bibliographic Details
Published in:Physical review letters 2019-07, Vol.123 (2)
Main Authors: Hester, Gavin, Nair, H. S., Reeder, T., Yahne, D. R., DeLazzer, T. N., Berges, L., Ziat, D., Neilson, J. R., Aczel, Adam A., Sala, Gabriele, Quilliam, J. A., Ross, K. A.
Format: Article
Language:English
Subjects:
antiferromagnetism
critical field
exchange interaction
Goldstone bosons
hard-core bosons
paramagnetism
phase diagrams
PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
triplon
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Summary:The quantum dimer magnet (QDM) is the canonical example of quantum magnetism. The QDM state consists of entangled nearest-neighbor spin dimers and often exhibits a field-induced triplon Bose-Einstein condensate (BEC) phase. We report on a new QDM in the strongly spin-orbit coupled, distorted honeycomb-lattice material Yb2Si2O7. Our single crystal neutron scattering, specific heat, and ultrasound velocity measurements reveal a gapped singlet ground state at zero field with sharp, dispersive excitations. We find a field-induced magnetically ordered phase reminiscent of a BEC phase, with exceptionally low critical fields of Hc1 ~ 0.4 and Hc2 ~ 1.4 T. Using inelastic neutron scattering in an applied magnetic field we observe a Goldstone mode (gapless to within δE=0.037 meV) that persists throughout the entire field-induced magnetically ordered phase, suggestive of the spontaneous breaking of U(1) symmetry expected for a triplon BEC. However, in contrast to other well-known cases of this phase, the high-field (μ0H≥1.2 T) part of the phase diagram in Yb2Si2O7 is interrupted by an unusual regime signaled by a change in the field dependence of the ultrasound velocity and magnetization, as well as the disappearance of a sharp anomaly in the specific heat. Finally, these measurements raise the question of how anisotropy in strongly spin-orbit coupled materials modifies the field induced phases of QDMs.
ISSN:0031-9007
1079-7114