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Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 19: Correlated Electrons: Quantum-Critical Phenomena

TT 19.11: Talk

Tuesday, February 26, 2008, 17:00–17:15, H 3010

Quantum Critical Spin Dynamics of a Cu(II) S=1/2 antiferromagnetic Heisenberg chain studied by 13C-NMR spectroscopy — •H. Kühne1, H.-H. Klauss1, J. Litterst2, S. Grossjohann3, W. Brenig3, A.P. Reyes4, P.L. Kuhns4, C.P. Landee5, M.M. Turnbull5, H.-J. Grafe6, B. Büchner6, and J. Haase61Institut für Festkörperphysik, TU Dresden — 2Institut für Physik der Kondensierten Materie, TU Braunschweig — 3Institut für Theoretische Physik, TU Braunschweig — 4NHMFL, FSU, Tallahassee, USA — 5DPC, Clark University, Worcester, USA — 6Leibniz-Institut für Werkstoffforschung, Dresden

The antiferromagnetic S=1/2 Heisenberg chain (S=1/2 AFHC) is a model system for quantum many-body physics. It allows a direct comparison between exact theoretical results and experiment for ground state properties and excitations. Cu(C4H4N2)(NO3)2 (CuPzN) is a very good experimental realization of the unperturbed S=1/2 AFHC [1,2]. In this compound we study the low energy spin dynamics by means of NMR. We measured the nuclear spin-lattice relaxation rate T1−1 of 13C as a function of temperature in a wide external magnetic field range from 2T to 28T, with an emphasis on the vicinity of the quantum critical point (QCP) at 14T. The experimental data are in good agreement with Quantum Monte Carlo calculations and clearly show critical behavior at low temperatures, i.e. a divergence of T1−1 at 14T and the linear opening of an energy gap for magnetic excitations with higher external fields. [1] P. Hammar et al., PRB. 59, 1008 (1999). [2] M.B. Stone et al., PRL 91, 037205 (2003).

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