NMR Insight to Quantum Magnets – pure and “healed” BaCuSi2O6, spin-1/2 chain β-TeVO4, and SrCu2(BO3)2 –
- 日 時：2019年5月24日（金）14:00 – 16:00
- 場 所：京都大学 理学部 6号館 571会議室
- 演 者：Professor Raivo Stern（National Institute of Chemical Physics & Biophysics, Estonia）
Ancient pigment, Han Purple (BaCuSi2O6) is a valuable model material for studying Bose-Einstein condensation (BEC) of magnons in high magnetic fields. We have characterized the BEC phase by Cu and Si NMR at 50 mK and around 23-27 T. In parallel, our density-functional calculations have resulted in a magnetic model with two types of nonequivalent spin dimers, in excellent agreement with the 63,65Cu NMR data, implying also the lack of magnetic frustration in BaCuSi2O6.* The “healed” Sr0.1Ba0.9CuSi2O6 with suppressed structural phase transition and just single set of dimers at low-T is a new extension of this study.**
For a frustrated zigzag spin-1/2 chain compound β-TeVO4, we verify the absence of the structural phase transition and address the possible existence of the high field low-T nematic phase.***
The spin-dimer antiferromagnet SrCu2(BO3)2 is the most prominent realization of the Shastry-Sutherland lattice model. We performed NMR measurements in pulsed magnetic fields up to 72 T using 11B nuclei.**** We observed a transition from a high-temperature, paramagnetic state to a low-T, commensurate superstructure of field-induced spin-dimer triplets on the 1/3 magnetization plateau. Our approach to measure broadband NMR in pulsed magnetic fields opens the door not only to the exploration of the higher-field groundstates of SrCu2(BO3)2, but also to studies of many other quantum magnets with complex interactions that stabilize new phases of matter in very strong magnetic fields.
* V.V. Mazurenko, M.V. Valentyuk, R. Stern, A.A. Tsirlin, PRL 112, 107202 (2014).
** P. Puphal, D. Sheptyakov, N. van Well, L. Postulka, I. Heinmaa, F. Ritter, W. Assmus, B. Wolf, M. Lang, H. O. Jeschke, R. Valenti, R. Stern, C. Rüegg, C. Krellner, PRB 93, 174121 (2016).
*** F. Weickert, N. Harrison, B.L. Scott, M. Jaime, A. Leitmäe, I. Heinmaa, R. Stern, O. Janson, H. Berger, H. Rosner, A. A. Tsirlin, PRB 94, 064403 (2016).
**** J. Kohlrautz, J. Haase, E.L. Green, Z. T. Zhang, J. Wosnitza, T. Herrmannsdörfer, H.A. Dabkowska, B.D. Gaulin, R. Stern, H. Kühne, J. Magn. Reson. 271, 52 (2016).