Entanglement in the pseudogap regime of cuprate superconductors

We find a strongly enhanced entanglement within the pseudogap regime of the Hubbard model. This entanglement is estimated from the quantum Fisher information and, avoiding the ill-conditioned analytical continuation, the quantum variance. Both are lower bounds for the actual entanglement that can be calculated from the (antiferromagnetic) susceptibility, obtained here with the dynamical vertex approximation. Our results qualitatively agree with experimental neutron scattering experiments for various cuprates. Theory predicts a $\ln (1\mathrm{/}T)$ divergence of the entanglement for low temperatures $T$, which is however cut-off by the onset of superconductivity.