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TT: Fachverband Tiefe Temperaturen

TT 18: CE: Low-dimensional Systems - Materials 1

TT 18.5: Vortrag

Montag, 14. März 2011, 19:30–19:45, HSZ 201

Evidence for the opening of a spin gap in the Ca-doped S=1/2 spin chain compound SrCuO₂ probed by NMR — •Franziska Hammerath, Satoshi Nishimoto, Hans-Joachim Grafe, A.U.B. Wolter, Christian Hess, Vladislav Kataev, Patrick Ribeiro, S.-L. Drechsler, and Bernd Büchner — Institute for Solid State Research, IFW Dresden,

We present ⁶³Cu Nuclear Magnetic Resonance (NMR) measurements on undoped SrCuO₂ and Ca-doped Sr_0.9Ca_0.1CuO₂ single crystals. The crystal structure contains one dimensional CuO₂ double chains that are magnetically decoupled due to frustration. For SrCuO₂ the spin lattice relaxation rate T₁⁻¹ is temperature independent as it is expected for a one dimensional S=1/2 Heisenberg spin chain. Doping with nonmagnetic, isovalent Ca takes place on the Sr sites outside the spin chains, and should not affect the magnetic properties of the compound. It is therefore very surprising that we do observe a decrease of T₁⁻¹ in the Ca-doped sample for temperatures below 80K that clearly evidences the opening of a gap in the spin excitation spectrum. Density Matrix Renormalization Group (DMRG) calculations are presented to discuss the origin of this spin gap.