A spin–orbital-entangled quantum liquid on a honeycomb lattice

A quantum-liquid state of spin–orbital-entangled magnetic moments is observed in the 5 d -electron honeycomb iridate H 3 LiIr 2 O 6 , evidenced by the absence of magnetic ordering down to 0.05 kelvin. Honeycomb hosts quantum spin liquid When materials with interacting spins are cooled, magnetic stat...

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Veröffentlicht in:Nature (London) 2018-02, Vol.554 (7692), p.341-345
Hauptverfasser: Kitagawa, K., Takayama, T., Matsumoto, Y., Kato, A., Takano, R., Kishimoto, Y., Bette, S., Dinnebier, R., Jackeli, G., Takagi, H.
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Sprache:eng
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Zusammenfassung:A quantum-liquid state of spin–orbital-entangled magnetic moments is observed in the 5 d -electron honeycomb iridate H 3 LiIr 2 O 6 , evidenced by the absence of magnetic ordering down to 0.05 kelvin. Honeycomb hosts quantum spin liquid When materials with interacting spins are cooled, magnetic states with long-range ordering usually emerge. However, quantum effects have been predicted to prevent long-range ordering all the way down to temperatures close to absolute zero in materials known as quantum spin liquids, where the term 'liquid' refers to the disordered state of the spins. The realization of such a state in a material with a honeycomb lattice, such as graphene, is expected to also reveal topological excitations. Hidenori Takagi and colleagues demonstrate a quantum-spin-liquid state in the 5 d honeycomb iridate H 3 LiIrO 6 , which shows no magnetic ordering down to 0.05 kelvin. Signatures of unusual excitations suggest that this material is a topological quantum-spin-liquid candidate. The honeycomb lattice is one of the simplest lattice structures. Electrons and spins on this simple lattice, however, often form exotic phases with non-trivial excitations. Massless Dirac fermions can emerge out of itinerant electrons, as demonstrated experimentally in graphene 1 , and a topological quantum spin liquid with exotic quasiparticles can be realized in spin-1/2 magnets, as proposed theoretically in the Kitaev model 2 . The quantum spin liquid is a long-sought exotic state of matter, in which interacting spins remain quantum-disordered without spontaneous symmetry breaking 3 . The Kitaev model describes one example of a quantum spin liquid, and can be solved exactly by introducing two types of Majorana fermion 2 . Realizing a Kitaev model in the laboratory, however, remains a challenge in materials science. Mott insulators with a honeycomb lattice of spin–orbital-entangled pseudospin-1/2 moments have been proposed 4 , including the 5 d -electron systems α-Na 2 IrO 3 (ref. 5 ) and α-Li 2 IrO 3 (ref. 6 ) and the 4 d -electron system α-RuCl 3 (ref. 7 ). However, these candidates were found to magnetically order rather than form a liquid at sufficiently low temperatures 8 , 9 , 10 , owing to non-Kitaev interactions 6 , 11 , 12 , 13 . Here we report a quantum-liquid state of pseudospin-1/2 moments in the 5 d -electron honeycomb compound H 3 LiIr 2 O 6 . This iridate does not display magnetic ordering down to 0.05 kelvin, despite an interaction energy of about 10
ISSN:0028-0836
1476-4687
DOI:10.1038/nature25482