Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 20: Correlated Electrons - Poster Session
TT 20.23: Poster
Mittwoch, 28. März 2007, 14:00–17:45, Poster A
High-Field NMR Relaxation Rates in Spin-1/2 Heisenberg-Chains — •Simon Großjohann1, Wolfram Brenig1, Hannes Kühne2, and Hans-Henning Klauß2 — 1Institut für Theoretische Physik, Technische Universität Braunschweig, D-31806 Braunschweig, Germany — 2Institut für Physik der Kondensierten Materie, Technische Universität Braunschweig, D-38106 Braunschweig, Germany
We study the critical dynamics of the one-dimensional antiferromagnetic spin-1/2 Heisenberg chain across the field-driven quantum phase transition into the fully polarized state at saturation field. Using a Quantum-Monte-Carlo approach based on the the Stochastic Series Expansion we evaluate the low-temperature transverse and longitudinal imaginary-time spin-correlation functions and perform analytic continuation to the frequency domain by Maximum-Entropy methods. Results will be presented in the thermodynamic limit for the temperature T, magnetic-field B, and momentum dependence of the dynamic structure factor. In particular we analyze these results in terms of the transverse nuclear-magnetic relaxation time T1(T,B). We observe a clear signature of quantum critical slowing-down, leading to an enhanced relaxation in the vicinity of the saturation field as well as relaxation from gapful excitations only above criticality. Finally, we compare our calculations with recent high-field 1/T1 NMR-data as observed on CuPzN and find satisfying agreement for all temperatures and magnetic fields investigated.