Instability of a quantum spin liquid in an organic triangular-lattice antiferromagnet

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Quantum liquids—known to be realized in 3He, 4He and electronsin metals—generally exhibit instabilities unforeseen under classical Newtonian dynamics, such as the superfluid and superconducting transitions. Recently, a new quantum liquid, now known as the quantum spin liquid, has been discovered in frustrated antiferromagnetic spin-1/2 systems1,2. In this state, quantum fluctuations of spins prevent classical antiferromagnetic ordering even at absolute zero, similar to the situation in the well-known quantum liquids. A fundamental question that has remained open is whether instabilities other than classical ordering can occur in a quantum spin liquid, as well as in the well-known quantum liquids. Here we demonstrate experimentally that a quantum spin liquid in an organic triangular-lattice antiferromagnet undergoes an instability involving symmetry breaking and/or topological ordering3, possibly giving rise to a new quantum state of matter. Our result reveals a new variety of quantum-liquid instability, which might become a comparable concept to the already-known fermion-liquid instabilities (such as Bardeen–Cooper–Schrieffer pairing and Peierls instability) and boson-liquid instability (Bose–Einstein condensation).

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Figure 1: Crystal structure of EtMe3Sb[Pd(dmit)2]2.
Figure 2: Temperature dependence of the 13C nuclear spin-lattice relaxation rate of EtMe3Sb[Pd(dmit)2]2.
Figure 3: Stretching exponent obtained from the 13C nuclear spin-lattice relaxation curves.
Figure 4: 13C-NMR spectra of EtMe3Sb[Pd(dmit)2]2 at several ultralow temperatures measured in a dilution refrigerator.


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We acknowledge helpful discussions with K. Kanoda, M. Tamura and Y. Shimizu. We thank F. Kagawa for helpful suggestions for improving of the manuscript. This work was supported by Grant-In-Aid for Scientific Research from MEXT, Japan (numbers 16GS0219, 18740199, 19052005 and 21740255).

Author information

T.I. designed the experiments, and carried out the NMR measurements, data analysis and discussion; A.O. and S.M. provided experimental support and suggestions; R.K. prepared the single crystals of EtMe3Sb[Pd(dmit)2]2 with selective substitution of the 13C isotope and gave several suggestions; T.I. wrote, and all authors commented on, the manuscript.

Correspondence to T. Itou.

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Itou, T., Oyamada, A., Maegawa, S. et al. Instability of a quantum spin liquid in an organic triangular-lattice antiferromagnet. Nature Phys 6, 673–676 (2010) doi:10.1038/nphys1715

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