Optical diode effect: exploration of large effects and application to antiferromagnetic domain imaging*

The optical absorption of ordinary materials is not changed by reversing the direction of light propagation. In contrast, when space-inversion and time-reversal symmetries of materials are both broken, the optical absorption for two counter-propagating light beams can be different [1,2]. This unconventional optical phenomenon, often called the optical diode (OD) effect by analogy with the semiconductor diode, has attracted interest for potential applications in novel nonreciprocal optical devices. Recent intensive studies have led to observations of the OD effect in many materials and over a wide range of wavelengths [1-5]. For the visible to near-infrared light range, however, the reported OD signals have usually been small [5] or require high magnetic fields to amplify the magnitude [4].

We are exploring materials that exhibit a large OD effect in the visible to near-infrared range. In this presentation, I will present our strategy for exploring such candidate materials. I will then present our recent achievements in the discovery of large visible-light OD signals in the antiferromagnet Bi₂CuO₄ [6]. In contrast to most previous observations, the large OD signals of Bi₂CuO₄ appear spontaneously in the absence of external fields. Furthermore, by switching multiple antiferromagnetic domains in Bi₂CuO₄ with an external field, we were able to demonstrate a three-level control of optical transparency. We will also present the results of even larger near-infrared OD signals in other antiferromagnets. Furthermore, we will show that the OD effect can be used to visualize the antiferromagnetic domains [6,7].

 

[1] G. L. J. A. Rikken et al., Nature, 390, 493 (1997).

[2] T. Arima, J. Phys.: Condens. Matter, 20, 434211 (2008).

[3] I. Kézsmárki et al., Nat. Commun. 5, 3203 (2014).

[4] S. Toyoda et al., PRL 115, 267207 (2015)

[5] T. Sato et al., PRL 124, 217402 (2020).

[6] K. Kimura et al., Nat. Commun. 13, 697 (2022).

[7] K. Kimura et al., Commun. Mater. 1, 39 (2020).