NMR evidence for a two-step phase separation in Nd1.85Ce0.15CuO4-delta.
By Cu NMR we studied the spin and charge structure in Nd(2-x)Ce(x)CuO(4-delta). For x=0.15, starting from a superconducting sample, the low temperature magnetic order in the sample reoxygenated under 1 bar oxygen at 900 degrees C reveals a peculiar modulation of the internal field, indicative of a phase characterized by large charge droplets ("blob" phase). By prolonged reoxygenation at 4 bars the blobs break up and the spin structure changes to that of an ordered antiferromagnet. We conclude that the superconductivity in the n-type systems competes with a genuine type I Mott-insulating state.
Kamerlingh Onnes Laboratory, Leiden University, POB 9504, 2300 RA Leiden, The Netherlands.
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Bakharev
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