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TT: Fachverband Tiefe Temperaturen

TT 44: Poster Session Correlated Electrons

TT 44.20: Poster

Donnerstag, 17. März 2011, 10:00–13:00, P1

Quantum critical dynamics in the one-dimensional spin chain systems CuPzN and (phzH)₂CuCl₄ — •H. Kühne^1,3, M. Günther¹, H.-H. Klauss¹, A.A. Zvyagin², J. Litterst³, S. Grossjohann⁴, W. Brenig⁴, A.P. Reyes⁵, P.L. Kuhns⁵, C.P. Landee⁶, and M.M. Turnbull⁶ — ¹IFP,TU Dresden — ²ILTPE,Kharkov,Ukraine — ³IPKM,TU Braunschweig — ⁴IThP,TU Braunschweig — ⁵NHMFL,Tallahassee,USA — ⁶DoP,Worcester,USA

We present a comprehensive NMR study of the field-driven quantum phase transitions in the spin=1/2 chain systems CuPzN and (phzH)₂CuCl₄. The static and dynamic experimental NMR properties are compared with both quantum Monte Carlo calculations and Luttinger liquid theory. CuPzN is known to be one of the best realizations of the antiferromagnetic S=1/2 Heisenberg chain (AFHC) model with a low coupling constant J. The zero temperature saturation field B_c = 14.6 T corresponds to a quantum critical point, where the system is driven from a Luttinger liquid state to ferromagnetic polarization. In the vicinity of this point in the corresponding B- and T- parameter space, a divergent behavior of the nuclear ¹3C-spin-lattice relaxation rate is observed and in good agreement with theory. (phzH)₂CuCl₄ is a recently synthesized spin chain system. ¹H- and ³5Cl-NMR experiments yield a field- and temperature dependent behavior of 1/T₁ similar to that of CuPzN. But, in contrast, a pronounced second maximum is observed at about 3/4 of the saturation field B_c = 12.2 T. This effect is not found in the local or macroscopic magnetization, suggesting a more complicated magnetic interaction scheme.