A hidden non-dipolar magnetic order parameter in Sr$_{2}$IrO$_{4}$ observed using nonlinear optical measurements

Iridium oxides are predicted to host a variety of exotic electronic phases arising from the interplay of electron correlations and spin-orbit coupling. There is particular interest in Sr$_{2}$IrO$_{4}$ owing to its striking structural and electronic similarities to the parent compound of high-Tc cuprates La$_{2}$CuO$_{4}$, which is further strengthened by the recent observation of Fermi arcs with a pseudogap behavior in doped Sr$_{2}$IrO$_{4}$ [1]. In this talk we report evidence of a previously hidden non-dipolar order parameter in Sr$_{2}$IrO$_{4}$ using low temperature nonlinear optical generation techniques [2,3]. We will discuss the significance of this novel order parameter in the context of cuprate high-Tc superconductivity and present comparative studies on non-perovskite families of iridium oxides. \\[4pt] [1] Y.K. Kim et. al, Science, 345, 187(2014)\\[0pt] [2] D. H. Torchinsky et. al, Rev. Sci. Instrum. 85, 083102(2014)\\[0pt] [3] D. H. Torchinsky et. al, arXiv 1411.0783(2014)