Observation of a ferro-rotational order coupled with second-order nonlinear optical fields
Observation of a ferro-rotational order coupled with second-order nonlinear optical fields
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DOI：
10.1038/s41567-019-0695-1
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发表时间：
2020-01-01
期刊：
影响因子：
19.6
通讯作者：
Zhao, Liuyan
中科院分区：
文献类型：
--
作者：
Jin, Wencan;Drueke, Elizabeth;Zhao, Liuyan
铁序可以根据序参量的对称性来分类，目前已经观察到铁电序、铁磁序和铁环面序。铁转动阶数（1-3）是最后需要识别的铁铁质，具有矢量阶数参数，其阶数参数在时间反转和空间反转操作下均为轴向量不变量。这一阶与极涡(4)、巨磁电耦合(5)和自旋旋驱动的铁电性(6)等许多现象密切相关，但迄今为止很少受到关注。在这里，我们利用高灵敏度的旋转各向异性二次谐波产生，利用电四极子对二次谐波产生的贡献，直接耦合到ii型多铁质原型RbFe(MoO4)(2)中的中心对称铁旋转顺序。我们发现，在临界温度T-c接近195 K时，具有相反铁旋转矢量的两个域态出现了不同的种群，并逐渐演化到较低温度时达到均匀比例。此外，我们已经确定了铁旋转序相变为弱一阶，并揭示了其耦合场是感应电四极二次谐波产生和入射基场的独特组合。作者利用光谱学证明了RbFe(MoO4)(2)具有铁旋转相。这是有待观察的铁有序的最终形式。
Ferroic orders can be classified by the symmetry of their order parameters, and ferroelectric, ferromagnetic and ferro-toroidal orders have already been observed. The ferro-rotational order(1-3), whose order parameter is an axial vector invariant under both time-reversal and spatial-inversion operations, is the final ferroic to be identified and has a vector order parameter. This order is closely related to a number of phenomena such as polar vortices(4), giant magnetoelectric coupling(5) and spin-helicity-driven ferroelectricity(6), but it has received little attention so far. Here, using high-sensitivity rotational-anisotropy second-harmonic generation, we have exploited the electric quadrupole contribution to the second-harmonic generation to directly couple to this centrosymmetric ferro-rotational order in an archetype of type-II multiferroics, RbFe(MoO4)(2). We found that two domain states with opposite ferro-rotational vectors emerge with distinct populations at the critical temperature T-c approximate to 195 K and gradually evolve to reach an even ratio at lower temperatures. Moreover, we have identified the ferro-rotational order phase transition as weakly first order and have revealed its coupling field as a unique combination of the induced electric quadrupole second-harmonic generation and the incident fundamental electric fields.The authors use optical spectroscopy to show that RbFe(MoO4)(2) hosts a ferro-rotational phase. This is the final form of ferroic order to be observed.