Berlin 2005 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique
TT 16.70: Poster
Samstag, 5. März 2005, 11:00–16:30, Poster TU C
Dimerization pattern or two-dimensional spin systems with spin phonon coupling in the adiabatic limit — •Carsten Aits1, Ute Löw1, and Andreas Klümper2 — 1Universität zu Köln, Institut für Theoretische Physik, Zülpicher Str.77, D-50937 Köln — 2Bergische Universität Wuppertal, Theoretische Physik, D-42097 Wuppertal
Little is known about the ground state phase diagram of two-dimensional spin systems with spin phonon coupling. In the adiabatic limit, however, they correspond to spin models with inhomogeneous couplings. In contrast to the one-dimensional case, where the dimerization pattern is unique, it is not clear how the two-dimensional lattice responds to a non-vanishing spin phonon coupling. As far as the S=1/2 Heisenberg model is concerned, different choices of inhomogenous patterns of couplings lead to rather different ground state properties with magnetic energy gain that may or may not compete with the energy loss of the phonon system.
We apply a loop algorithm in continuous Trotter time to clarify which distortion pattern is energetically favored. Our approach is twofold. First, we extrapolate the ground state energies and magnetizations for various patterns of alternating couplings and analyze whether a transition to a gapped state appears. Second, we consider an expansion of the free energy of the distorted models at the point of vanishing distortion. In the adiabatic limit, this corresponds to an analysis of spin layers coupled to three dimensional phonons at finite temperatures. We determine the coefficients of the leading order from the (Euclidean) dynamical dimer correlation functions, which are directly accessible within our method.