  Nonlinear optics plays important roles in the research of fundamental physics
and the applications of highperformance 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, 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 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.
