Crystal growth and transport properties of spin ladder compounds La_4+4nCu_8+2nO_14+8n (n = 2, 3)

Here we summarize recent progress on the study of spin ladder compounds, La₂Cu₂O₅ (four-leg) and La₈Cu₇O₁₉ (five-leg), n = 2 and 3 members of the homologous series La_4+4nCu_8+2nO_14+8n. Following the successful crystal growth of La₂Cu₂O₅, we grew a pure-phase five-leg system La₈Cu₇O₁₉ by a modified slow cooling method. The room-temperature resistivity of the as-grown La₈Cu₇O₁₉ crystal was 1.9 Ω cm, which is much lower than that of the La₂Cu₂O₅ crystals (≈ 1.7 × 10³ Ω cm). A significant drop in the resistivity (11.0 mΩ cm at 300 K) was observed upon hole doping by means of high oxygen-pressure annealing, although no transition was observed from the semiconducting behavior. In addition, a new crystal growth method to enhance hole doping level of La₂Cu₂O₅ is shown.