Observation of all-in type tetrahedral displacements in nonmagnetic pyrochlore niobates

Torigoe, Shuhei*; Ishimoto, Yutaro*; Aoishi, Yuhei*; Murakawa, Hiroshi*; Matsumura, Daiju   ; Yoshii, Kenji  ; Yoneda, Yasuhiro   ; Nishihata, Yasuo; Kodama, Katsuaki   ; Tomiyasu, Keisuke*; Ikeda, Kazutaka*; Nakao, Hironori*; Nogami, Yoshio*; Ikeda, Naoshi*; Otomo, Toshiya*; Hanasaki, Noriaki*

We observed all-in type Nb tetrahedral displacement in nonmagnetic pyrochlore niobates ANbO (A = NdCa and YCa) through the analysis of the neutron pair distribution function and the extended X-ray absorption function spectroscopy. The all-in type Nb tetrahedral displacement, which has the character of a charge singlet state, is driven by the formation of the bonding orbital. The diffuse scattering in the X-ray diffraction, which has the resonant component in the Nb 3 edge, indicates that the all-in type Nb tetrahedral displacement has the periodicity with its short-range correlation.