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TT: Tiefe Temperaturen

TT 13: Systeme korrelierter Elektronen: Theorie I

TT 13.8: Talk

Tuesday, March 12, 2002, 16:30–16:45, H20

Spectral Densities of 1D Quantum Antiferromagnetic S=1/2 Systems — •Kai P. Schmidt¹, Christian Knetter¹, Markus Grüninger², and Götz S. Uhrig¹ — ¹Institut für theoretische Physik, Universität zu Köln, Zülpicher Str.77, D-50937 Köln, Germany — ²II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany

We are using optimally chosen continuous unitary transformations to calculate spectral densities for the S=1/2 two-leg spin ladder and spin chains.

The importance and the influence of the four spin cyclic exchange term on spectral densities of spin ladder systems is discussed. Motivated by recent experiments we investigate modulated ladder and chain systems. In addition, we calculate spectral weights for uniform Heisenberg chains indicating that the essential point is not the fractionality of the elementary excitations (spinons) but the proper description of multi-particle excitations[1].

Our results render a direct comparison between theory and experiment possible. They are relevant for optical absorption [2] , Raman spectroscopy [3] and neutron scattering.

[1] Knetter et al., Phys.Rev.Lett. 87, 167204 (2001)
[2] Windt et al., Phys.Rev.Lett. 87, 127002 (2001)
[3] Schmidt et al., Eur.Phys.Lett. 56, issue 6 (2001)