Electric field-induced nonreciprocal directional dichroism in a time-reversal-odd antiferromagnet

Abstract

Antiferromagnets with broken time-reversal (T) symmetry (T-odd antiferromagnets) have gained extensive attention, mainly due to their ferromagnet-like behavior despite the absence of net magnetization. However, certain types of T-odd antiferromagnets remain inaccessible by the typical ferromagnet-like phenomena (e.g., anomalous Hall effect). One such system is characterized by a T-odd scalar quantity, the magnetic toroidal monopole. To access the broken T symmetry in such a system, we employ a unique nonreciprocal optical phenomenon, electric field-induced nonreciprocal directional dichroism (E-induced NDD). We successfully detected signals of E-induced NDD in a T-odd antiferromagnet, Co2SiO4, whose magnetic structure is characterized by the magnetic toroidal monopole. Furthermore, by spatially resolving the E-induced NDD, we visualized spatial distributions of a pair of domain states related to one another by the T operation. The domain imaging revealed the inversion of the domain pattern by applying a magnetic field, which is explained by trilinear coupling attributed to the piezomagnetic effect. Our observation of E-induced NDD provides a unique approach to accessing the order parameter in T-odd antiferromagnets.

16 pages, 12 figures

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