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New Disturbance-Resistant Quantum Liquid State Discovered in a Copper-Oxide Magnetic Body (Press Release)

Release Date
04 May, 2012
  • BL02B1 (Single Crystal Structure Analysis)
  • BL02B2 (Powder Diffraction)

University of Tokyo
Nagoya University
Osaka University
Japan Atomic Energy Agency

Results obtained: It was ascertained that a new quantum liquid state can be achieved by controlling the orbit-spin cooperative phenomena of copper atoms' electrons.
Novelty (what is new): We discovered the first instance, in a copper oxide, of a quantum liquid state that defies transition into orbital ordering (Jahn-Teller phase transition) even at very low temperatures. The spin liquid state realized in this system exhibits, contrary to conventional knowledge, strong resistance against disturbances.
Implication to society / future perspective: The discovery of a material that exhibits a disturbance-resistant quantum liquid state is considered to provide a guideline for the development of materials required to construct the infrastructure for controlling quantum information (typically a quantum computer).

The quantum liquid, typically represented by superconductivity, has become an important research objective both for applications and basic research.

Up to the present, the quantum liquid state that develops within magnetic bodies has been considered sensitive to disturbances. A research group, led by Associate Professor Satoru Nakatsuji at the Institute for Solid State Physics (director: Yasuhiro Iye) of the University of Tokyo, in collaboration with Nagoya University, Center for Quantum Science and Technology under Extreme Conditions (Osaka University), California State University, Japan Atomic Energy Agency, University of the Ryukyus, Bandung Institute of Technology, National Institute of Standards and Technology, University of Maryland, and Johns Hopkins University, conducted research on copper oxide magnetic bodies*1 with inherent structural disturbances. The team discovered a formation of a new quantum state that defied ordering, even at very low temperatures. The preservation of a liquid state can be interpreted as a result of spin-orbit cooperative phenomena (spin is a degree of freedom inherent to an electron). The experimental results indicate that the newly discovered phenomenon constitutes a very disturbance-resistant quantum liquid state, the understanding of which is expected to serve as a guideline for future substance/material developments.

"Spin-orbital short range order on a honeycomb based lattice"
S. Nakatsuji, K. Kuga, K. Kimura, R. Satake, N. Katayama, E. Nishibori, H. Sawa, R. Ishii, M. Hagiwara, F. Bridges, T. U. Ito, W. Higemoto, Y. Karaki, M. Halim, A. A. Nugroho, J. A. Rodriguez-Rivera, M. A. Green, C. Broholm
Science 336 (6081), 559-563, published online 4 May 2012


Fig. 1.
Fig. 1.

Crystal structure of Ba3CuSb2O9: Copper ions (red) form a honeycomb-like short-range order

Fig. 2.
Fig. 2.

Two possible quantum states produced by the spin-orbit cooperative phenomenon: (upper) a spin resonance state produced by a ring-shaped electron orbital order; (lower) a spin-orbit resonance state (similar to a π-electron resonance state in a benzene molecule).

Fig. 3.
Fig. 3.

The energy gaps generated by a spin liquid state, as revealed by the neutron-scattering technique. The vertical axis corresponds to energy, and the horizontal axis to wave number in (reciprocal) space. Generation of the energy gaps is considered to impart stability to the spin liquid state, making it robust against the effect of impurity and other disturbances.

*1 Magnetic body, magnetic order, and ferromagnetism

The magnetic body is a piece of material that contains tiny magnets (or spins) resulting from the rotational motion of each electron inside. A normal cooling procedure applied to a magnetic body gives rise to the development of magnetic order: a macroscopic number of electron spins line up in order in some pattern or other. Magnetic bodies are broadly classified into three categories: ferromagnetic bodies, such as Fe, Co, and Ni (normally called a magnet), that exhibits macroscopic magnetization; antiferromagnetic bodies, in which magnetization is cancelled within the body; and paramagnetic bodies, in which the spins inside do not develop an orderly orientational arrangement.

*2 Spin liquid and quantum spin liquid
Spin liquid refers to a state in which the spin orientation of each electron—bound to an ion that gives rise to magnetism—is fluctuating spatially as well as temporarily, without maintaining a fixed orientation. If the body maintains its spin liquid state even at the temperature of absolute zero, i.e. orderly orientation can not be established due to quantum fluctuation, it is called a quantum spin liquid.

Glossary_fig1*3 Geometric frustration
Each arrow symbol at the apexes of the regular triangle represents a spin. Each arrow may take an up or down orientation, but every pair of adjacent spins must be inversely oriented to each other (antiferromagnetic). These two requirements hinder the establishment of a uniquely-determined arrangement, impeding the spins. As this example illustrates, magnetic bodies with a triangle-based structure can not provide all of the spin pairs with preferable mutual relations (this deadlock is called geometric frustration).

For more information, please contact:
  Dr. Satoru Nakatsuji (The University of Tokyo)

  Prof. Hiroshi Sawa (Nagoya University)

  Prof. Masayuki Hagiwara (Osaka University)

  Dr. Wataru Higemoto (Japan Atomic Energy Agency )

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