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Strong anisotropy of superexchange in the copper-oxygen chains of La_{14-x}Ca_{x}Cu_{24}O_{41}

V. Kataev·K. -Y. Choi·M. Grüninger·U. Ammerahl·B. Büchner·A. Freimuth·A. Revcolevschi
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Abstract

Electron spin resonance data of Cu^{2+} ions in La_{14-x}Ca_{x}Cu_{24}O_{41} 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 ~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 degree 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.

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V. Kataev, K. -Y. Choi, M. Grüninger, U. Ammerahl, B. Büchner, A. Freimuth, A. Revcolevschi. 2001-01-04. Strong anisotropy of superexchange in the copper-oxygen chains of La_{14-x}Ca_{x}Cu_{24}O_{41}. https://doi.org/10.1103/physrevlett.86.2882

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