17ONMR study of the local charge state in the hole-dopedCu2O3two-leg spin-ladderA14Cu24O41(A14=La6Ca8,Sr14,Sr11Ca3,Sr6Ca8)Journal Articles
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abstract
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-ladder
layer of hole-doped A_{14}Cu_{24}O_{41} changes dramatically above a certain
temperature, T*. This temperature, T*, decreases with additional doping and is
correlated with the magnetic crossover from the spin gap regime to the
paramagnetic regime. We demonstrate that these changes in ^{17}\nu_{Q} are
consistent with an increase in the effective hole concentration in the
Cu_{2}O_{3} two-leg ladder above T*. The effective hole concentration increases
primarily in the oxygen 2p\sigma orbitals.