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We have performed an angle-resolved photoemission study on PrBa2Cu307 (Prl23) and PrBa2Cu408 (Prl24) which have hole-doped Cu-O chains. Dispersive features with one-dimensional (ID) character are observed in Prl23 and Prl24 and are attributed to signals from the hole-doped Cu-O chains which are approximately 1/4-filled. While, in Prl23, the ID feature loses its spectral weight near the Fermi level (EF), it crosses EF in Prl24. These results suggest that, while the hole-doped Cu-O single chains in Prl23 have instability to charge ordering, the hole-doped Cu-O double chains in Prl24 can get rid of it.

The superconducting transition temperature (T c ), magnetic susceptibility and pressure depehdence of T c were measured for (Y1−xPrx)2Ba4Cu7O15−δ (x=0, 0.1, 0.4 and 0.6), all of which were synthesized under high O2 pressure. The degree of depression of T c due to Pr doping in the 247 phase is closer to that found in the Pr-doped 124 phase than that in the Pr-doped 123 phase. A variation of the lattice parameter suggested that doped Pr is in the valence state of 3+, but magnetic susceptibility data indicated a mixed valence state for the Pr ion in the 247 phase. We found that the pressure dependence of T c , dT c /dP, changes its sign gradually from a positive to negative one with increasing Pr concentration. In particular, the value of dT c /dP for the x=0.6 sample reached −18 K/GPa.

The superconducting transition temperature (T c ) was measured as a function of pressure up to 2 GPa for Y2Ba4(Cu1−xCox)7O15−δ (x=0,0.03 and 0.05) which was synthesized under high O2 pressures. The unit cell of 247-compound is built up from the alternative stacking of the 123 and 124 blocks. Thus, single and double chains appear alternatively with each other. The value of T c decreased with increasing Co content x. Irrespective of Co contents, a large enhancement of T c was observed with increasing pressure up to 1 GPa. The T c tends to be saturated in the pressure above 1 GPa. We found from neutron diffraction analysis that the doped Co atoms occupy only the Cu site in the single chain.