Fujiwara K, Fukada Y, Okuda Y, Seimiya R, Ikeda N, Yokoyama K, Yu H, Koshihara S, Okimoto Y
Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama, 700-8530, Japan.
National Institutes for Quantum and Radiological Science and Technology (QST), 1-1-1 Kouto, Sayo, Hyogo, 679-5148, Japan.
Sci Rep. 2021 Feb 19;11(1):4277. doi: 10.1038/s41598-021-83655-6.
We report the first observation of room temperature spontaneous electric polarization in an electronic ferroelectric material, a YbFeO single crystal. The observation was based on second harmonic generation (SHG), a nonlinear optical process. Tensor analysis of the SHG signal revealed that this material has a polar charge superstructure with Cm symmetry. This result settles the long-term discussion on the uncertainty about electronic ferroelectric properties, including the charge order structure. We present a complete picture of the polar charge ordering of this material via consistent results from two different characterization methods. The SHG signal shows the same temperature dependence as the superlattice signal observed in neutron diffraction experiments. These results prove ferroelectric coupling to electron ordering in YbFeO, which results in electronic ferroelectricity which is enabled by the real space ordering of iron cations with different valences. The existence of electronic ferroelectricity holds promise for future electronics technologies where devices run a thousand times faster than frequency of the present CPU (a few gigahertz) embedded in smartphones, etc.
我们报道了在一种电子铁电材料——YbFeO单晶中首次观察到室温下的自发电极化。该观察基于二次谐波产生（SHG）这一非线性光学过程。对SHG信号的张量分析表明，这种材料具有具有Cm对称性的极性电荷超结构。这一结果解决了关于电子铁电性质（包括电荷有序结构）不确定性的长期讨论。我们通过两种不同表征方法的一致结果，给出了这种材料极性电荷有序的完整图像。SHG信号显示出与中子衍射实验中观察到的超晶格信号相同的温度依赖性。这些结果证明了YbFeO中铁电与电子有序的耦合，这导致了电子铁电性，其由不同价态铁阳离子的实空间有序所促成。电子铁电性的存在为未来的电子技术带来了希望，在这些技术中，设备的运行速度比智能手机等中嵌入的当前CPU（几吉赫兹）的频率快一千倍。
