NMR evidence for higher-order multipole order parameters in NpO2

Y. Tokunaga, D. Aoki, Y. Homma, S. Kambe, H. Sakai, S. Ikeda, T. Fujimoto, R. E. Walstedt, H. Yasuoka, E. Yamamoto, A. Nakamura, Y. Shiokawa

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37 Citations (Scopus)


We report a microscopic investigation of multipolar order parameters in the ordered state of NpO2 conducted via O17 NMR on a single crystal. From the angular dependence of hyperfine fields at O17 nuclei, we have obtained clear evidence for the appearance of field-induced antiferro-octupolar as well as field-induced antiferro-dipolar moments below T0=26K. We have also observed oscillatory spin-echo decay, which is well understood in terms of small electric field gradients created by antiferro-quadrupolar ordering. This reveals that the quadrupolar order parameter is directly observable by means of NMR. The present NMR studies provide definitive support for a proposed longitudinal triple-q type octupolar-quadrupolar ordering model for NpO2.

Original languageEnglish
Article number257601
JournalPhysical Review Letters
Issue number25
Publication statusPublished - 2006


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