Skin Effect of Nonlinear Optical Responses in Antiferromagnets

TL;DR

This paper reveals a surface-localized skin effect in nonlinear optical responses of antiferromagnets, challenging the traditional view that such responses are uniform throughout noncentrosymmetric crystals, and suggests new device applications.

Contribution

It uncovers a surface-specific nonlinear optical response in antiferromagnets caused by local inversion symmetry preservation, a novel phenomenon not previously recognized.

Findings

Nonlinear responses are localized near surfaces in antiferromagnets.

The effect is linked to the local preservation of inversion symmetry.

Potential for new antiferromagnetic optospintronics devices.

Abstract

Nonlinear optics plays important roles in the research of fundamental physics and the applications of high-performance optoelectronic devices. The bulk nonlinear optical responses arise from the uniform light absorption in noncentrosymmetric crystals, and hence are usually considered to be the collective phenomena of all atoms. Here we show, in contrast to this common expectation, the nonlinear optical responses in antiferromagnets can be selectively accumulated near the surfaces, representing a skin effect. This is because the inversion symmetry, despite being broken globally by magnetism, is barely violated locally deeply inside these antiferromagnets. Using A-type layered antiferromagnets as the representatives, we predict that the spatial-dependent nonlinear optical responses, such as bulk photovoltaic effect (BPVE) and second harmonic generation (SHG), are notable in the top- and bottom-most layers and decay rapidly when moving away from the surfaces. Such a phenomenon is strongly associated with the antiferromagnetism and exists in a broad range of antiferromagnets composed of centrosymmetric sublattices, offering promising device applications using these antiferromagnets. Our work uncovers a previously overlooked property of nonlinear optical responses and opens new opportunities for high-performance antiferromagnetic optospintronics.