Spin Gap in the Zigzag Spin-1/2 Chain Cuprate Sr0.9Ca0.1CuO2
F. Hammerath, S. Nishimoto, H.-J. Grafe, A. U. B. Wolter, V. Kataev, P. Ribeiro, C. Hess, S.-L. Drechsler, B. Büchner
DOI 10.1103/PhysRevLett.107.017203 · Physical Review Letters
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Abstract
We report a comparative study of Cu63 nuclear magnetic resonance spin lattice relaxation rates T1−1 on undoped SrCuO2 and Ca-doped Sr0.9Ca0.1CuO2 spin chain compounds. A temperature independent T1−1 is observed for SrCuO2 as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T1−1 for T<90 K in the Ca-doped sample evidencing the opening of a spin gap. The data analysis within the J1−J2 Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J2-exchange coupling as a possible cause of the spin gap.
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