Münster 1997 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

AM: Magnetismus

AM 9: Postersitzung Fürstenberghaus

AM 9.8: Poster

Tuesday, March 18, 1997, 09:30–12:30, F"u

Accurate mapping of quantum Heisenberg magnetic models on strong-coupling spin wave systems — •Bang-Gui Liu and Gerd Czycholl — Institut für Theoretische Physik, Universität Bremen, Postfach 330 440, D-28334 Bremen

An infinite-U term is introduced into the spin-wave-transformed hamiltonian of quantum Heisenberg magnetic models. This term removes the unphysical spin wave states and absorbs the high power terms from S_i⁺S_j⁻ as well. The resultant strong-coupling spin-wave hamiltonians are accurately equivalent to the original spin hamiltonians. On-site U levels are studied. Within a simple Hubbard approximation we obtain results for the sublattice magnetization which correspond to the RPA and are substantial improvements on the results of conventional (linear and nonlinear) spin wave theories in the whole temperature region. Our ground state spectral factors are improved substantially and our ground state energies are lower than those of RPA and the spin wave theories. We also study the bosonic hamiltonians in a Mori-Zwanzig projection method, obtaining lower ground state energy. This bosonic hamiltonian should be advantageous in developing more sophisticated approximation for the quantum Heisenberg magnetic models.