title: Structural distortion-induced magnetoelastic locking in Sr(2)IrO(4) revealed through nonlinear optical harmonic generation.
abstract: We report a global structural distortion in Sr_{2}IrO_{4} using spatially resolved optical second and third harmonic generation rotational anisotropy measurements. A symmetry lowering from an I4_{1}/acd to I4_{1}/a space group is observed both above and below the Néel temperature that arises from a staggered tetragonal distortion of the oxygen octahedra. By studying an effective superexchange Hamiltonian that accounts for this lowered symmetry, we find that perfect locking between the octahedral rotation and magnetic moment canting angles can persist even in the presence of large noncubic local distortions. Our results explain the origin of the forbidden Bragg peaks recently observed in neutron diffraction experiments and reconcile the observations of strong tetragonal distortion and perfect magnetoelastic locking in Sr_{2}IrO_{4}.
authors: Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA.|Department of Physics, California Institute of Technology, Pasadena, California 91125, USA.
authors: D H
authors: DH
authors: Torchinsky
authors: Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA.|Department of Applied Physics, California Institute of Technology, Pasadena, California 91125, USA.
authors: H
authors: H
authors: Chu
authors: Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA.|Department of Physics, California Institute of Technology, Pasadena, California 91125, USA.
authors: L
authors: L
authors: Zhao
authors: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55116, USA.
authors: N B
authors: NB
authors: Perkins
authors: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55116, USA.
authors: Y
authors: Y
authors: Sizyuk
authors: Center for Advanced Materials, Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA.
authors: T
authors: T
authors: Qi
authors: Center for Advanced Materials, Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA.
authors: G
authors: G
authors: Cao
authors: Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA.|Department of Physics, California Institute of Technology, Pasadena, California 91125, USA.
authors: D
authors: D
authors: Hsieh