title: Strong anisotropy of superexchange in the copper-oxygen chains of La(14)-xCaxCu24O41.
abstract: Electron spin resonance data of Cu2+ ions in La(14)-xCaxCu24O41 single crystals (x = 9,11,12) reveal a very large width of the resonance line in the paramagnetic state. This signals an unusually strong anisotropy of approximately 10% of the isotropic Heisenberg superexchange in the Cu-O chains of this compound. The strong anisotropy can be explained by the specific geometry of two symmetrical 90 degrees Cu-O-Cu bonds, which boosts the importance of orbital degrees of freedom. Our data show the apparent limitations of the applicability of an isotropic Heisenberg model to the low-dimensional cuprates.
authors: II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.
authors: V
authors: V
authors: Kataev
authors: K Y
authors: KY
authors: Choi
authors: M
authors: M
authors: Grüninger
authors: U
authors: U
authors: Ammerahl
authors: B
authors: B
authors: Büchner
authors: A
authors: A
authors: Freimuth
authors: A
authors: A
authors: Revcolevschi