Dresden 2006 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

TT: Tiefe Temperaturen

TT 25: Correlated Electrons - Poster Session

TT 25.42: Poster

Mittwoch, 29. März 2006, 14:30–18:30, P1

Orbital Waves versus Vibronic Excitations — •Kai P. Schmidt¹, Markus Grüninger², and Götz S. Uhrig³ — ¹Institute of Theoretical Physics, École Polytechnique Fédérale de Lausanne, CH 1015 Lausanne, Switzerland — ²II. Physikalisches Institut der RWTH Aachen, Templergraben 55, 52056 Aachen, Germany — ³Theoretische Physik, Geb. 38, FR 7.1, Universität des Saarlandes, D-66123 Saarbrücken, Germany

A large number of transition-metal compounds show orbital ordering at low temperatures. But the experimental observation of the corresponding elementary excitations of an orbitally ordered state, the so-called orbital waves (orbitons), turned out to be rather difficult, and a watertight experimental proof for the existence of orbitons is still lacking. It is therefore natural to ask whether other degrees of freedom are involved in transition-metal compounds which complicates the search for orbital waves. In this contribution the coupling of orbital and lattice degrees of freedom is investigated. We calculated the kinetic and the spectral properties of the orbital waves for a one-dimensional toy-model. The elementary excitations are orbital-wave-like for small orbiton-phonon coupling. In contrast, the excitations are vibronic when the coupling between orbital and lattice degrees of freedom is large. The most interesting case is the crossover regime at intermediate couplings. Here the most important spectral contribution is a continuum build by one orbiton and by one phonon. Surprisingly, the spectral density displays rather sharp resonances inside the continuum which form a shadow-like image of the one-orbiton dispersion.