Nonmonotonic Pressure Dependence of the Lattice Parameter a in the Quasi-one-dimensional Superconductor Pr2Ba4Cu7O15−δ

In the quasi-one-dimensional superconductor, Pr2Ba4Cu7O15−δ, we found that the lattice parameter, a increased against pressure, starting at 2.0 GPa at approximately 300 K. This result suggests that the two-dimensional inter-conducting-chain interaction along the a axis is most enhanced at approximately 2.0 GPa. To discuss the dimensionality, we also measured the resistance under magnetic fields up to 14 T, because magneto-resistance is induced when a system changes from one-dimensional to two-dimensional.