Soft phonon mode coupled with antiferromagnetic order in incipient-ferroelectric Mott insulators SrBaMnO

初期強誘電モット絶縁体SrBaMnOにおける反強磁性に対応するソフトフォノンモード

酒井 英明*; 藤岡 淳*; 福田 竜生  ; Bahramy, M. S.*; 奥山 大輔*; 有田 亮太郎*; 有馬 孝尚*; Baron, A. Q. R.*; 田口 康二郎*; 十倉 好紀*

Sakai, Hideaki*; Fujioka, Jun*; Fukuda, Tatsuo; Bahramy, M. S.*; Okuyama, Daisuke*; Arita, Ryotaro*; Arima, Takahisa*; Baron, A. Q. R.*; Taguchi, Yasujiro*; Tokura, Yoshinori*

Infrared optical and inelastic X-ray scattering spectra have been systematically investigated in combination with first-principles calculations for paraelectric and antiferromagnetic perovskite SrBaMnO single crystals, which are close to a ferroelectric transition arising from off-center displacement of magnetic Mn ions. One optical phonon rapidly softens toward zero frequency at room temperature with increasing . This soft-mode behavior is also reproduced by the first-principles calculations, from which we have predicted the vibration mode of all the optical phonons. Below the antiferromagnetic-transition temperature, the soft mode hardens with decreasing temperature and then resoftens toward the lowest temperature.