Absence of Jahn-Teller transition in the hexagonal Ba3CuSb2O9 single crystal

Naoyuki Katayama, Kenta Kimura, Yibo Han, Joji Nasu, Natalia Drichko, Yoshiki Nakanishi, Mario Halim, Yuki Ishiguro, Ryuta Satake, Eiji Nishibori, Masahito Yoshizawa, Takehito Nakano, Yasuo Nozue, Yusuke Wakabayashi, Sumio Ishihara, Masayuki Hagiwara, Hiroshi Sawa, Satoru Nakatsujij

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose-Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Moreover, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin-orbital entanglement in FeSc2S4. To confirm this exotic ground state, experiments based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin-orbital liquid candidate, 6H-Ba3CuSb2O9, and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn-Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn-Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. We discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin-orbital entangled quantum liquid state.

Original languageEnglish
Pages (from-to)9305-9309
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number30
Publication statusPublished - 2015 Jul 28


  • BaCuSbO
  • Jahn-Teller transition
  • Quantum liquid state
  • Spin-orbital entanglement
  • Synchrotron X-ray diffraction

ASJC Scopus subject areas

  • General


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