Symmetry breaking of in-plane anisotropic magnetoresistance with temperature in La-doped Sr2IrO4 films

Electron-doped Sr2IrO4 has been the subject of much recent attention because of its similarities with hol-edoped La2CuO4. However, direct evidence of its superconductivity has not yet been observed, which has led to various unresolved issues related to this material. In this study, a 14-nm-thick La-doped Sr2IrO4 film was grown on a (001) SrTiO3 substrate. We found that the fourfold component of the in-plane anisotropic magnetoresistance disappears and is replaced by a twofold symmetry as the temperature increases. Variable-temperature x-ray diffraction and spatially resolved optical second-harmonic generation experiments eliminate the possibility of crystal structural distortion. The temperature dependence of direct current magnetization measurements indicates that a change in the spin structure may account for the symmetry breaking, similar to the nematic ordering of iron-based and other superconductors. Remarkably, the transition temperature of the symmetry breaking is well consistent with the previously reported onset (50 K) of the low-energy gap in K-doped Sr2IrO4 observed by scanning tunneling spectroscopy. Our results provide a perspective on these materials that helps elucidate the nature of magnetic interactions and explores the expected superconductivity of iridates.