title: Spin gap in the zigzag spin-1/2 chain cuprate Sr(0.9)Ca(0.1)CuO(2).
abstract: We report a comparative study of (63)Cu nuclear magnetic resonance spin lattice relaxation rates T(1)(-1) on undoped SrCuO(2) and Ca-doped Sr(0.9)Ca(0.1)CuO(2) spin chain compounds. A temperature independent T(1)(-1) is observed for SrCuO(2) as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T(1)(-1) for T<90 K in the Ca-doped sample evidencing the opening of a spin gap. The data analysis within the J(1)-J(2) Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J(2)-exchange coupling as a possible cause of the spin gap.
authors.affiliation: Leibniz Institute for Solid State and Materials Research IFW Dresden, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Hammerath
authors.forename: S
authors.initials: S
authors.lastname: Nishimoto
authors.forename: H-J
authors.initials: HJ
authors.lastname: Grafe
authors.forename: A U B
authors.initials: AU
authors.lastname: Wolter
authors.forename: V
authors.initials: V
authors.lastname: Kataev
authors.forename: P
authors.initials: P
authors.lastname: Ribeiro
authors.forename: C
authors.initials: C
authors.lastname: Hess
authors.forename: S-L
authors.initials: SL
authors.lastname: Drechsler
authors.forename: B
authors.initials: B
authors.lastname: Büchner