Regular-Triangle Trimer and Charge Order Preserving the Anderson Condition in the Pyrochlore Structure of CsW$_2$O$_6

• Main Authors: Okamoto, Yoshihiko, Amano, Haruki, Katayama, Naoyuki, Sawa, Hiroshi, Niki, Kenta, Mitoka, Rikuto, Harima, Hisatomo, Hasegawa, Takumi, Ogita, Norio, Tanaka, Yu, Takigawa, Masashi, Yokoyama, Yasunori, Takehana, Kanji, Imanaka, Yasutaka, Nakamura, Yuto, Kishida, Hideo, Takenaka, Koshi
• Format: Journal Article
• Language: English
• Published: 19.06.2020
• Subjects: Physics - Materials Science; Physics - Strongly Correlated Electrons
• DOI: 10.48550/arxiv.2006.11053

Nat. Commun. 11, 3144 (2020) Since the discovery of the Verwey transition in magnetite, transition metal compounds with pyrochlore structures have been intensively studied as a platform for realizing remarkable electronic phase transitions. We report the discovery of a unique phase transition that preserves the cubic symmetry of the beta-pyrochlore oxide CsW$_2$O$_6$, where each of W 5d electrons are confined in regular-triangle W3 trimers. This trimer formation is an unprecedented self-organization of d electrons, which can be resolved into a charge order satisfying the Anderson condition in a nontrivial way, orbital order caused by the distortion of WO6 octahedra, and the formation of a spin-singlet pair in a regular-triangle trimer. Electronic instability due to the unusual three-dimensional nesting of Fermi surfaces and the localized nature of the 5d electrons characteristic of the pyrochlore oxides were found to play important roles in this unique charge-orbital-spin coupled phenomenon.