17O NMR Study of the Local Charge State in the Hole Doped Cu2O3 Two-Leg Spin-Ladder A14Cu24O41 (A=La6Ca8, Sr14, Sr11Ca3, Sr6Ca8)

摘要

NMR measurements of the ^{17}O nuclear quadrupole interactions, ^{17}\nu_{Q},show that the charge environment of the S=1/2 Cu_{2}O_{3} two-leg spin-ladderlayer of hole-doped A_{14}Cu_{24}O_{41} changes dramatically above a certaintemperature, T*. This temperature, T*, decreases with additional doping and iscorrelated with the magnetic crossover from the spin gap regime to theparamagnetic regime. We demonstrate that these changes in ^{17}\nu_{Q} areconsistent with an increase in the effective hole concentration in theCu_{2}O_{3} two-leg ladder above T*. The effective hole concentration increasesprimarily in the oxygen 2p\sigma orbitals.