Competing spin-orbital singlet states in the 4d4 honeycomb ruthenate Ag3LiRu2O6

T. Takayama*, M. Blankenhorn, J. Bertinshaw, D. Haskel, N.A. Bogdanov, K. Kitagawa, A.N. Yaresko, A. Krajewska, S. Bette, G. McNally, A.S. Gibbs, Y. Matsumoto, D.P. Sari, I. Watanabe, G. Fabbris, W. Bi, T.I. Larkin, K.S. Rabinovich, A.V. Boris, H. IshiiH. Yamaoka, T. Irifune, R. Bewley, C.J. Ridley, C.L. Bull, R. Dinnebier, B. Keimer, H. Takagi

*Corresponding author for this work

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When spin-orbit-entangled d electrons reside on a honeycomb lattice, rich quantum states are anticipated to emerge, as exemplified by the d5 Kitaev materials. Distinct yet equally intriguing physics may be realized with a d-electron count other than d5. The magnetization, 7Li-nuclear magnetic resonance (NMR), and inelastic neutron scattering measurements, together with the quantum chemistry calculation, indicate that the layered ruthenate Ag3LiRu2O6 with d4Ru4+ ions at ambient pressure forms a honeycomb lattice of spin-orbit-entangled singlets, which is a playground for frustrated excitonic magnetism. Under pressure, the singlet state does not develop the expected excitonic magnetism, but two successive transitions to other nonmagnetic phases were found in 7Li-NMR, neutron diffraction, and x-ray absorption fine structure measurements, first to an intermediate phase with moderate distortion of honeycomb lattice and eventually to a high-pressure phase with very short Ru-Ru dimer bonds. While the strong dimerization in the high-pressure phase originates from a molecular orbital formation as in the sister compound Li2RuO3, we argue that the intermediate phase represents a spin-orbit-coupled singlet dimer state which is stabilized by the admixture of upper-lying Jeff=1-derived states via a pseudo-Jahn-Teller effect. The emergence of competing electronic phases demonstrates rich spin-orbital physics of d4 honeycomb compounds, and this finding paves the way for realization of unconventional magnetism.
Original languageEnglish
Article number043079
Number of pages13
JournalPhysical Review Research
Issue number4
Early online date7 Nov 2022
Publication statusPublished - 1 Dec 2022


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