The Cluster-Perturbation-Theory and its Application to Strongly-Correlated Materials

We present a technique whereby the standard restriction of quantum-mechanic many-body simulations to small clusters of 10 to 1000 sites can be overcome by the systematic use of a so-called cluster perturbation theory. In principle, this facilitates the accurate numerical solution of the macroscopic, i.e. infinite-size system. These calculations have become feasible only with the recent advance of high-performance computers. Angular-resolved photoemission data on various strongly-correlated materials are analyzed as a specific example, via a method that extends exact-diagonalization analysis to the infinite lattice by means of a perturbation in the intercluster hopping. We apply this method to relate photoemission data to different phases of high-Tc materials, namely (i) the so-called stripe phase of LaSrCuO and LaNdSrCuO, in which doped holes organize themselves in quasi-one-dimensional structures, (ii) the insulating phase of SrCuOCl, (iii) and the Fermi surface geometry of the overdoped Bi2Sr2CaCu2O8+ δ compound. The computational effort, which is necessary to address this problem and the performance that we have achieved, is detailed.