17O and 63Cu NMR in Undoped and Hole Doped Cu2O3 Two-Leg Spin Ladder A14Cu24O41 (A14=La6Ca8,Sr14,Sr11Ca3)

We conducted the first 17O NMR in the S=1/2 Cu2O3 two-leg spin ladder, and probed the low energy spin excitations of various momentum transfers up to 850 K. These measurements clearly demonstrate the crossover from the spin gap to the paramagnetic regime. In the hole-doped ladders, the crossover is accompanied by changes in electric field gradient tensors and charge transport properties, suggesting interplay between spin and charge degrees of freedom.