Theoretical investigations of the phase diagram of highTc superconductors
One essential new point of the Forschergruppe (FG) is to study the
hole and electrondoped phase diagram of the hightemperature
superconductors (HTSC) in a tightknit effort between experiment and
theory. In the first funding period, we have already made use of this
unique possibility, namely using input from a variety of different
experiments (neutron scattering, photoemission) on one and the same
material to construct a phenomenology of the HTSC, i.e. aiming at the
key question ``which boson drives the superconducting pairing''. This
concerted effort, together with a variational cluster solution of
the Hubbard model gave reason to believe that the correct physics of
the HTSC is that of ``doping into a Mott insulator'', i.e. the physics
of strong electronic correlations. It is the central aim of our
present proposal to substantiate this belief employing both T=0 and
finiteT cluster techniques, in combination with a new scheme we
have developed for extracting twoparticle (i.e. spin and charge)
excitations. Together with our already working schemes (VCA and DCA)
for calculating singleparticle excitations, this gives us a
previously not available complete dynamical information of the HTSC
compounds under study. This information will be used to clarify the
still unresolved issue of what is ``universal'' and what is ``material
specific''. The following topics, which are central for arriving at a
``universal picture'' will be addressed: the (finiteT) phase
diagram for Hubbardtype models also with additional orbital degrees
of freedom, the physics of the pseudogap and the effects of
inhomogeneities (stripes, static and fluctuating, etc.) and defects.
