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arXiv · 2011.11662

Spin-orbit-enhanced magnetic surface second-harmonic generation in Sr$_2$IrO$_4$

K. L. Seyler·A. de la Torre·Z. Porter·E. Zoghlin·R. Polski·M. Nguyen·S. Nadj-Perge·S. D. Wilson·D. Hsieh
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Abstract

An anomalous optical second-harmonic generation (SHG) signal was previously reported in Sr$_2$IrO$_4$ and attributed to a hidden odd-parity bulk magnetic state. Here we investigate the origin of this SHG signal using a combination of bulk magnetic susceptibility, magnetic-field-dependent SHG rotational anisotropy, and overlapping wide-field SHG imaging and atomic force microscopy measurements. We find that the anomalous SHG signal exhibits a two-fold rotational symmetry as a function of in-plane magnetic field orientation that is associated with a crystallographic distortion. We also show a change in SHG signal across step edges that tracks the bulk antiferromagnetic stacking pattern. While we do not rule out the existence of hidden order in Sr$_2$IrO$_4$, our results altogether show that the anomalous SHG signal in parent Sr$_2$IrO$_4$ originates instead from a surface-magnetization-induced electric-dipole process that is enhanced by strong spin-orbit coupling.

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K. L. Seyler, A. de la Torre, Z. Porter, E. Zoghlin, R. Polski, M. Nguyen, S. Nadj-Perge, S. D. Wilson, D. Hsieh. 2020-11-23. Spin-orbit-enhanced magnetic surface second-harmonic generation in Sr$_2$IrO$_4$. https://doi.org/10.1103/physrevb.102.201113

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