Emergent spin-1 Haldane gap and ferroelectricity in a frustrated spin- ladder

フラストレートしたスピンラダー物質におけるスピン1ハルデンギャップと強誘電性

上田 宏*; 小野田 繁樹*; 山口 泰弘*; 木村 剛*; 吉澤 大智*; 森岡 俊晶*; 萩原 政幸*; 萩原 雅人*   ; 左右田 稔*; 益田 隆嗣*; 榊原 俊郎*; 富安 啓輔*; 河村 聖子   ; 中島 健次  ; 梶本 亮一  ; 中村 充孝   ; 稲村 泰弘  ; Reynolds, N.*; Frontzek, M.*; White, J. S.*; 長谷 正司*; 安井 幸夫*

Ueda, Hiroshi*; Onoda, Shigeki*; Yamaguchi, Yasuhiro*; Kimura, Tsuyoshi*; Yoshizawa, Daichi*; Morioka, Toshiaki*; Hagiwara, Masayuki*; Hagihara, Masato*; Soda, Minoru*; Masuda, Takatsugu*; Sakakibara, Toshiro*; Tomiyasu, Keisuke*; Kawamura, Seiko; Nakajima, Kenji; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Reynolds, N.*; Frontzek, M.*; White, J. S.*; Hase, Masashi*; Yasui, Yukio*

We report experimental and theoretical evidence that RbCuMoO has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled frustrated spin- chains and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya interaction are identified in inelastic neutron-scattering and electron spin resonance spectra. A tiny magnetic field generates ferroelectricity without closing the spin gap, indicating a unique class of ferroelectricity induced by a vector spin chirality order.