Formation of orbital molecules on a pyrochlore lattice induced by A-O bond covalency

A. Krajewska; A. Yaresko; J. Nuss; A. S. Gibbs; S. Bette; M. Blankenhorn; R. E. Dinnebier; D. P. Sari; I. Watanabe; J. Bertinshaw; H. Gretarsson; K. Ishii; D. Matsumura; T. Tsuji; M. Isobe; B. Keimer; H. Takagi; T. Takayama

arXiv · 2111.05057

Formation of orbital molecules on a pyrochlore lattice induced by A-O bond covalency

A. Krajewska·A. Yaresko·J. Nuss·A. S. Gibbs·S. Bette·M. Blankenhorn·R. E. Dinnebier·D. P. Sari·I. Watanabe·J. Bertinshaw·H. Gretarsson·K. Ishii·D. Matsumura·T. Tsuji·M. Isobe·B. Keimer·H. Takagi·T. Takayama

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Abstract

The pyrochlore ruthenate In$_2$Ru$_2$O$_7$ displays a subtle competition between spin-orbital entanglement and molecular orbital formation. At room temperature, a spin-orbit-entangled singlet state was identified. With decreasing temperature, In$_2$Ru$_2$O$_7$ undergoes multiple structural transitions and eventually forms a nonmagnetic ground state with semi-isolated Ru$_2$O units on the pyrochlore lattice. The dominant hopping through the Ru-O-Ru linkage leads to molecular orbital formation within the Ru$_2$O units. This molecular orbital formation is unique in that it involves the O$^{2-}$ anions, unlike the transition-metal dimers observed in systems with edge-sharing octahedra. We argue that the covalent character of In-O bonds plays a pivotal role in the structural transitions and molecular orbital formation and such bonding character of "$A$-site" ions is an important ingredient for electronic phase competition in complex transition metal oxides.

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A. Krajewska, A. Yaresko, J. Nuss, A. S. Gibbs, S. Bette, M. Blankenhorn, R. E. Dinnebier, D. P. Sari, I. Watanabe, J. Bertinshaw, H. Gretarsson, K. Ishii, D. Matsumura, T. Tsuji, M. Isobe, B. Keimer, H. Takagi, T. Takayama. 2021-11-09. Formation of orbital molecules on a pyrochlore lattice induced by A-O bond covalency. https://arxiv.org/abs/2111.05057

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