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TT: Fachverband Tiefe Temperaturen

TT 55: Correlated Electrons: Low-Dimensional Systems -Materials 2

TT 55.3: Vortrag

Donnerstag, 14. März 2013, 10:00–10:15, H21

Impurity effects in a S=1/2 Heisenberg spin chain probed by ⁶³Cu NMR — •Yannic Utz¹, Eva Maria Brüning¹, Franziska Hammerath¹, Christian Rudisch¹, Hans-Joachim Grafe¹, Ashwin Mohan¹, Romuald Saint-Martin², Alexandre Revcolevschi², Christian Hess¹, Satoshi Nishimoto¹, Stefan-Ludwig Drechsler¹, and Bernd Büchner¹ — ¹IFW Dresden, Germany — ²LPCES, Orsay, France

We present ⁶³Cu NMR measurements on undoped, Ni doped and Mg doped SrCuO₂ single crystals. SrCuO₂ is a good realization of a one-dimensional S=1/2 Heisenberg spin chain. This is confirmed by the theoretically-expected temperature independent NMR spin-lattice relaxation rate T₁⁻¹. Doping with Ni, which can be regarded as a S=1 impurity, has a major impact on the magnetic properties of the spin chains. On the one hand, this is manifested by unusual features in the NMR spectra below 100 K, revealing the existence of an impurity-induced local alternating magnetisation. On the other hand, exponentially decacying spin lattice relaxation rates towards low temperatures indicate the opening of a spin gap similar to Ca doped SrCuO₂ [1]. Mg doping (S=0) has, however, no influence on the magnetic properties of the spin chains. Neither the NMR spectra nor the spin lattice relaxation rates differ from those measured on pure SrCuO₂. While the different impact of Ni and Mg 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.
[1] F. Hammerath et al., Phys. Rev. Lett. 107, 017203 (2011).