Correlated Band Structure and the Ground-State Phase Diagram in High-TC Cuprates

We review results obtained with a recently proposed variational cluster approach (VCA) for the competition between d-wave superconductivity (dSC) and antiferromagnetism (AF) in the high-TC cuprates. Comparing the single-particle spectra of a two-dimensional Hubbard model with quantum Monte-Carlo (QMC) and experimental data, we verify that the VCA correctly treats the low-energy excitations. The cluster calculations reproduce the overall ground-state phase diagram of the high-temperature superconductors both for electronand hole-doping. In particular, they include salient features such as the enhanced robustness of the AF state in case of electron doping. For electronbut also for hole-doping, we clearly identify a tendency to phase separation into a mixed AF-dSC phase at low and a pure dSC-phase at high doping.