Lattice effect on the superexchange interaction in antiferromagnetic Bi$_2$Sr$_2$CaCu$_2$O$_8

The in-plane superexchange interaction $J$ of cuprate superconductors has long been suggested to be an important parameter for exploring their high-temperature superconductivity. The bilayer Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is the most studied system with high-quality single crystals in the wide doping range with the the same structure and phase. So far, the lattice parameter dependence of $J$ in its antiferromagnetic parent compound Bi$_2$Sr$_2$CaCu$_2$O$_{8}$ has not been established. By combining Raman scattering and x-ray diffraction techniques on the same sample in the same pressure environment, we obtain the evolution of both the two-magnon spectrum and the structural parameters with pressure up to nearly 30 GPa, The relationship between pressure or the in-plane lattice parameter and $J$ is thus established for Bi$_2$Sr$_2$CaCu$_2$O$_{8}$. Over the studied pressure range, superconductivity does not appear in this parent compound based on a sensitive magnetic measurement technique. The effects of pressure and chemical doping on the superexchange interaction and structure and their implications for superconductivity are discussed from the comparison of the obtained experimental data with the existing experiments. The results and findings provide valuable information for the understanding of superconductivity and the future theory developments for superconductivity in cuprates.