Terahertz time-domain spectroscopy of electromagnons in multiferroic perovskite manganites [Invited]
Terahertz time-domain spectroscopy of electromagnons in multiferroic perovskite manganites [Invited]
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DOI：
10.1364/josab.26.000a35
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发表时间：
2009-04
影响因子：
1.9
通讯作者：
N. Kida;Y. Takahashi;Jong-Seok Lee;Ryo Shimano;Yuichi Yamasaki;Yoshio Kaneko;Shin Miyahara;Nobuo Furukawa;Taka-hisa Arima;Yoshinori Tokura
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文献类型：
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作者：
N. Kida;Y. Takahashi;Jong-Seok Lee;Ryo Shimano;Yuichi Yamasaki;Yoshio Kaneko;Shin Miyahara;Nobuo Furukawa;Taka-hisa Arima;Yoshinori Tokura
最近对各种具有铁电和磁序的多铁性材料在太赫兹频率下的光谱研究揭示了可能出现一种新的集体激发，通常称为电磁子。它原本是磁性的，但它会响应光的电场分量而变得活跃。在这里，我们概述了我们在电磁子太赫兹时域光谱或电偶极子主动磁共振方面的最新进展，重点关注钙钛矿锰酸盐 - RMnO3（R 表示稀土离子）。通过使用一组完整的晶体取向测量光偏振依赖性，可以确定对所观察到的磁共振的各自的电和磁贡献。我们提取了各种自旋有序相的一般光学特征，包括 A 型反铁磁共线自旋有序相以及铁电 bc 和 ab 螺旋自旋有序相，这些特征是通过调整 R 的化学成分、温度和外部磁场来实现的。除了由光的磁场分量驱动的 Mn 离子的反铁磁共振之外，我们还阐明，即使在共线自旋有序相中，电磁子也仅对沿 a 轴偏振的光出现，并且其强度随着螺旋自旋有序的演化而增强，但与螺旋自旋平面的方向（bc 或 ab）无关，或者等效地与铁电极化 Ps 的方向（Ps∥c 或 Ps∥a）无关。通过将此处提供的系统实验数据与基于海森堡模型的理论考虑进行比较，讨论了在太赫兹频率下观察到的磁共振的可能起源。
Recent spectroscopic studies at terahertz frequencies for a variety of multiferroics endowed with both ferroelectric and magnetic orders have revealed the possible emergence of a new collective excitation, frequently referred to as electromagnon. It is magnetic in origin, but it becomes active in response to the electric field component of light. Here we give an overview of our recent advance in the terahertz time-domain spectroscopy of electromagnons, or electric-dipole active magnetic resonances, focused on perovskite manganites—RMnO3 (R denotes rare-earth ions). The respective electric and magnetic contributions to the observed magnetic resonance are firmly identified by the measurements of the light-polarization dependence using a complete set of the crystal orientations. We extract general optical features in a variety of the spin-ordered phases, including the A-type antiferromagnetic, collinear spin-ordered phase and the ferroelectric bc and ab spiral spin-ordered phases, which are realized by tuning the chemical composition of R, the temperature, and the external magnetic field. In addition to the antiferromagnetic resonances of Mn ions driven by the magnetic field component of light, we clarify that the electromagnon appears only for light that is polarized along the a axis, even in the collinear spin-ordered phase, and it grows in intensity with evolution of the spiral spin order but is independent of the direction of the spiral spin plane (bc or ab) or, equivalently, the direction of the ferroelectric polarization Ps (Ps∥c or Ps∥a). A possible origin of the observed magnetic resonances at terahertz frequencies is discussed by comparing the systematic experimental data presented here with theoretical considerations based on the Heisenberg model.