Pressure dependence of the superexchange interaction in antiferromagneticLa2CuO4

Using high-pressure Raman scattering, we have directly measured the pressure dependence of the in-plane superexchange interaction J in antiferromagnetic ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ between 1 bar and 100 kbar. We find that J has a substantially weaker pressure dependence than in conventional magnets. We also show that the Hubbard-model parameters describing the low-energy electronic structure are significantly influenced by out-of-plane compositional and structural variations. Finally, we show that the relationship between J and the Neél temperature ${\mathit{T}}_{\mathit{N}}$ is poorly described by current theory.