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TT: Fachverband Tiefe Temperaturen

TT 45: Correlated Electrons: Poster Session

TT 45.67: Poster

Donnerstag, 29. März 2012, 15:00–19:00, Poster B

NMR evidence for peculiar spin gaps in a doped S=1/2 Heisenberg spin chain — •Yannic Utz¹, Christian Rudisch¹, Franziska Hammerath¹, Hans-Joachim Grafe¹, Ashwin Mohan¹, Surjeet Singh², Romuald Saint-Martin³, Alexandre Revcolevschi³, Patrick Ribeiro¹, Christian Hess¹, Anja Wolter¹, Vladislav Kataev¹, Satoshi Nishimoto¹, Stefan-Ludwig Drechsler¹, and Bernd Büchner¹ — ¹IFW Dresden, Germany — ²Indian Institute of Science Education and Research, Pune, India — ³Laboratoire de Physico-Chimie de l’Etat Solide, Université Paris-Sud, Orsay, France

We present ⁶³Cu Nuclear Magnetic Resonance (NMR) measurements on undoped, Ca-doped and Ni-doped SrCuO₂ single crystals. SrCuO₂ is a good realization of a one-dimensional S=1/2 Heisenberg spin chain. This is manifested by the theoretically-expected temperature-independent NMR spin-lattice relaxation rate T₁⁻¹. In Sr_0.9Ca_0.1CuO₂ an exponential decrease of T₁⁻¹ below 90 K evidences the opening of a gap in the spin excitation spectrum, which amounts to Δ= 50 K [1]. DMRG calculations are presented to discuss the origin of this spin gap. New results on SrCu_0.99Ni_0.01O₂ also indicate the presence of a spin gap, which is twice as large as in Sr_0.9Ca_0.1CuO₂, despite the minor doping level of Ni compared to Ca. We discuss different possible impacts of Ca (S=0) and Ni (S=1) doping on structural and magnetic properties of the parent compound.
F. Hammerath et al., Phys. Rev. Lett. 107, 017203 (2011).