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TT: Fachverband Tiefe Temperaturen

TT 23: Low-Dimensional Systems: Other Materials

TT 23.2: Vortrag

Montag, 31. März 2014, 17:00–17:15, BEY 81

Nuclear Magnetic Resonance on S=1/2 Heisenberg Spin Chains under the Impact of Different Impurities — •Yannic Utz¹, Franziska Hammerath¹, Hans-Joachim Grafe¹, Ashwin Mohan¹, Neela Sekhar Beesetty², Romuald Saint-Martin², Alexandre Revcolevschi², Christian Hess¹, and Bernd Büchner¹ — ¹IFW Dresden, Germany — ²ILPCES - ICMMO, Université Paris-Sud, France

We present ⁶³Cu NMR measurements on single crystals of undoped, Ni doped and Zn doped SrCuO₂ and of Ni doped Sr₂CuO₃. While SrCuO₂ forms a double chain structure, the copper ions of Sr₂CuO₃ are arranged as single chains. Despite these structural differences, both are known to be good realizations of the antiferromagnetic S=1/2 Heisenberg chain. The measurements show that Ni doping (S=1) has a major impact on the magnetic properties of both spin chain systems. An unusual line broadening in the low temperature NMR spectra reveals the existence of an impurity-induced local alternating magnetization (LAM), and exponentially decaying spin-lattice relaxation rates T₁⁻¹ towards low temperatures indicate the opening of a spin gap similar to Ca-doped SrCuO₂ [1]. Zn doping (S=0), however, shows a similar impact on the NMR spectra, but the opening of a spin gap could not be observed. While the different impact of Ni and Zn doping on the spin chains could be explained by their different impurity spins, the opening of a spin gap in case of Ni doping is totally unexpected and not yet understood.
F. Hammerath et al., Phys. Rev. Lett. 107, 017203 (2011)