Non-centrosymmetric Sr${}_2$IrO${}_4$ obtained under High Pressure

Abstract

Sr${}_2$IrO${}_4$ with strong spin-orbit coupling (SOC) and Hubbard repulsion (U) hosts Mott insulating states. The similar crystal structure, magnetic and electronic properties, particularly the $d$-wave gap observed in Sr${}_2$IrO${}_4$ enhanced the analogies to cuprate high-$T_c$ superconductor, La${}_2$CuO${}_4$. The incomplete analogy was due to the lack of broken inversion symmetry phases observed in Sr${}_2$IrO${}_4$. Here, under high pressure and high temperature conditions, we report a non-centrosymmetric Sr${}_2$IrO${}_4$. The crystal structure and its noncentrosymmetric character were determined by single crystal X-ray diffraction and high-resolution scanning transmission electron microscopy (HR-STEM). The magnetic characterization confirms the Ir${}^{4+}$ with $S$ = 1/2 at low temperature in Sr${}_2$IrO${}_4$ with magnetic ordering occurred at around 86 K, where a larger moment is observed than the ambient pressure Sr${}_2$IrO${}_4$. Moreover, the resistivity measurement shows three-dimensional Mott variable-range hopping existed in the system. This non-centrosymmetric Sr${}_2$IrO${}_4$ phase appears to be a unique material to offer further understanding of high-$T_c$ superconductivity.