High-Temperature superconducting materials (HTSC) are characterized by
strong electronic correlations, which are responsible for a number of
fascinating anomalous physical properties. Depending on temperature
and doping, these materials show long-range ordered phases as well as
regions of strong but short-range fluctuations.
It is the central aim
of the present theory project to achieve a significantly improved
microscopic understanding of the HTSC and, in particular, of the
doping dependence of their phase diagram, focusing on the question
what is of general relevance'' and what is more
material-specific''. In this project we plan to apply and to further
develop two cluster methods in order to evaluate thermodynamic
properties, phase boundaries, and excitation spectra of common model
systems for the HTSC (one- and three-band Hubbard models).
should be carried out in close contact with the newly established
(DFG) Research Unit Doping dependence of phase transitions and
ordering phenomena in copper-oxide superconductors'', and the results
obtained within the present project should be compared with
experimental results of the other groups (inelastic neutron
scattering, angle-resolved photoemission-, tunneling-, and
Raman-spectroscopy). Some of the many questions related to the
physics of HTSC should be addressed in the present project: (i) the
competition between long-range ordered phases as well as the effects
of short-range fluctuations, (ii) the nature of the so-called
pseudogap: is it different in electron-doped materials?, (iii) the
phase diagram and the symmetry of the order parameter in
electron-doped compounds, (iv) the role of phonons in HTSC, and (v)
the anomalous behavior of the optical conductivity.
With the help of
the coordinated cooperation with the experimental groups of the
Research Unit we expect to understand the global phase diagram of
HTSC in the hole- and in the electron-doped compounds on the basis of
a unifying picture of a doped Mott insulator.