该研究团队展示了手性的电控制和由此产生的NiTiO3铁轴晶体短波长红外区域的电场诱导MChD (E-MChD)。研究人员利用在有和没有电场与磁场的情况下分别获得的吸收系数差对E-MChD进行了光谱测量。结果表明，在Ni2+ d-d磁偶极子跃迁对应的激发能附近观察到E-MChD。采用关于能态伪斯塔克分裂的MChD理论很好地解释了这一结果。因此，铁轴材料为实现手性相关现象的电气控制提供了平台。
据悉，在手性介质中，任何镜像对称性都被打破，这导致了其独特的物理性质，即天然旋光性。当电磁波通过放置在磁场中的手性介质传播时，折射率，或者等效的，电磁波所遇到的吸收取决于它是与磁场平行还是反平行传播。这种现象被称为磁手性二色性（Magnetic Chiral Dichroism，MChD），它是手性和磁性之间的特征相互作用。与手性类似，所谓的铁轴序，是晶体材料的一种涌现铁性态，也具有镜像对称破缺的特征。然而，与手性材料相反，在铁轴材料中，垂直于晶体主轴的镜像对称是允许的。换句话说，手性和手性特有的现象可以通过施加电场来打破剩余的镜像对称性来诱导。
附：英文原文
Title: Electric field–induced magnetochiral dichroism in a ferroaxial crystal
Author: Hayashida, Takeshi, Kimura, Kenta, Kimura, Tsuyoshi
Issue&Volume: 2023-8-17
Abstract: In a chiral medium, any mirror symmetries are broken, which induces unique physical properties represented by natural optical rotation. When electromagnetic waves propagate through a chiral medium placed in a magnetic field, the refractive index, or equivalently, the absorption encountered by the electromagnetic waves differs depending on whether it travels parallel or antiparallel to the magnetic field. Such a phenomenon is known as magnetochiral dichroism (MChD), which is the characteristic interplay between chirality and magnetism. Similar to chirality, the so-called ferroaxial order, an emergent ferroic state of crystalline materials, is also characterized by mirror symmetry breaking. In contrast to chiral materials, however, the mirror symmetry perpendicular to the crystalline principal axis is allowed in ferroaxial materials. In other words, chirality and thus phenomena unique to chirality can be induced by breaking the remaining mirror symmetry by applying an electric field. Here, we show electric control of chirality and resulting electric field–induced MChD (E-MChD) of the short-wavelength infrared region in a ferroaxial crystal, NiTiO3. We performed spectroscopy measurements of E-MChD by taking a difference of absorption coefficients obtained with and without electric and magnetic fields. As a result, E-MChD was observed around the excitation energy corresponding to Ni2+ d-d magnetic-dipole transitions. The result is nicely explained by adopting the theory of MChD concerning the pseudo-Stark splitting of the energy state. Ferroaxial materials therefore provide platforms to achieve electric control of chirality-related phenomena.
DOI: 10.1073/pnas.2303251120
Source: https://www.pnas.org/doi/10.1073/pnas.2303251120