Continuous evolution of the 2D Hubbard model from an insulator to a metal

We present Quantum-Monte-Carlo results for the momentum and frequency dependent spectral weight A(k, ω) showing the evolution from insulating to metallic behavior in the two-dimensional Hubbard model. As observed in recent photoemission experiments for cuprates, in both undoped and doped cases the electronic excitations display two rather similar general features, i.e. a quasiparticle (QP)-like dispersive band of small width of the order of the exchange interaction J and a broad valence- and conduction-band background. Arguments for one and the same many-body physics namely the continuous reduction of the spin-spin correlation length and related changes in the QP-spin correlations behind the continuous evolution to the metallic QP dispersion are given.