Charge-order pattern of the low-temperature phase from a monoclinic single domain of NaV
O
uniquely determined by resonant X-ray scattering
斜方晶ドメインからの共鳴X線散乱によりユニークに決定されたNaV
O
低温相の電荷秩序パターン
大和田 謙二; 藤井 保彦; 勝木 裕也*; 村岡 次郎*; 中尾 裕則*; 村上 洋一; 澤 博*; 仁宮 恵美*; 礒部 正彦*; 上田 寛*
Owada, Kenji; Fujii, Yasuhiko; Katsuki, Yuya*; Muraoka, Jiro*; Nakao, Hironori*; Murakami, Yoichi; Sawa, Hiroshi*; Ninomiya, Emi*; Isobe, Masahiko*; Ueda, Yutaka*
共鳴X線散乱をNaV
O
のT
以下で現れる斜方晶ドメインに適用することで低温相の電荷秩序パターンをユニークにAAA'A'であると決定した。これらの結果により、A, A'をイジングスピンに対応させることができ、NaV
O
のT
における「悪魔の階段」的相転移を説明できるようになった。
The present resonant X-ray scattering has been performed on a monoclinically-split single domain of NaV
O
. The observation of a critically enhanced contrast between V
and V
ions has led us to the unequivocal conclusion of the charge-order pattern of low-temperature phase of NaV
O
below
= 35 K. In spite of the possible four types of configuration of the zig-zag-type charge-order patterns in the
-plane (A, A', B and B'), the stacking sequence along the
-axis is determined as the AAA'A' type by comparison with model calculations. By assigning the A and A' configurations to Ising spins, one can reasonably explain the previously discovered "devil's staircase"-type behavior with respect to the modulation of layer-stacking sequences at high pressures and low temperatures, which clearly resembles the global phase diagram theoretically predicted by the ANNNI model.