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. Haase6 — 1Institut 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).