Spin-orbit-enhanced magnetic surface second-harmonic generation in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Sr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi>Ir</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>
Kyle L. Seyler, A. de la Torre, Zach Porter, Eli Zoghlin, Robert Polski, Minh-Hai Nguyen, Stevan Nadj-Perge, Stephen D. Wilson, David Hsieh
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 twofold 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.