title: Absence of Jahn-Teller transition in the hexagonal Ba3CuSb2O9 single crystal.
abstract: 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.
authors.affiliation: Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan; katayama@mcr.nuap.nagoya-u.ac.jp.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Katayama
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan;
authors.forename: Kenta
authors.initials: K
authors.lastname: Kimura
authors.affiliation: Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka University, Osaka 560-8531, Japan; Wuhan National High Magnetic Field Center, Huzhong University of Science and Technology, Wuhan 430074, China;
authors.forename: Yibo
authors.initials: Y
authors.lastname: Han
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan;
authors.forename: Joji
authors.initials: J
authors.lastname: Nasu
authors.affiliation: Institute for Quantum Matter (IQM) and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218;
authors.forename: Natalia
authors.initials: N
authors.lastname: Drichko
authors.affiliation: Graduate School of Engineering, Iwate University, Morioka 020-8551, Japan;
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Nakanishi
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan;
authors.forename: Mario
authors.initials: M
authors.lastname: Halim
authors.affiliation: Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan;
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ishiguro
authors.affiliation: Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan;
authors.forename: Ryuta
authors.initials: R
authors.lastname: Satake
authors.affiliation: Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan;
authors.forename: Eiji
authors.initials: E
authors.lastname: Nishibori
authors.affiliation: Graduate School of Engineering, Iwate University, Morioka 020-8551, Japan;
authors.forename: Masahito
authors.initials: M
authors.lastname: Yoshizawa
authors.affiliation: Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;
authors.forename: Takehito
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Nozue
authors.affiliation: Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan;
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Wakabayashi
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan;
authors.forename: Sumio
authors.initials: S
authors.lastname: Ishihara
authors.affiliation: Center for Advanced High Magnetic Field Science, Graduate School of Science, Osaka University, Osaka 560-8531, Japan;
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hagiwara
authors.affiliation: Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan;
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sawa
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan; PRESTO (Precursory Research for Embryonic Science and Technology), Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakatsuji
keywords: Ba3CuSb2O9; Jahn–Teller transition; quantum liquid state; spin-orbital entanglement; synchrotron X-ray diffraction