Controlling the chiral degree of freedom in matter has long been an important issue for many fields of science. The spin-spiral order, which exhibits a strong magnetoelectric coupling, gives rise to chirality irrespective of the atomic arrangement of matter. Here, we report the resonantly enhanced natural optical activity on the electrically active magnetic excitation, that is, electromagnon, in multiferroic cupric oxide. The electric field control of the natural optical activity is demonstrated through magnetically induced chirality endowed with magnetoelectric coupling. These optical properties inherent to multiferroics may lead to optical devices based on the control of chirality.

长期以来，控制物质的手性自由度一直是许多科学领域的重要课题。表现出强磁电耦合的自旋-螺旋顺序，无论物质的原子排列如何，都会产生手性。在这里，我们报告了在多铁氧化铜中，对电活性磁激发，即电磁子，共振增强的自然光学活性。通过具有磁电耦合的磁感应手性证明了自然光学活性的电场控制。多铁性化合物固有的这些光学性质可导致基于手性控制的光学器件。