Crystal structure and physical properties of the spin-1/2 two leg ladder system, Sr14−xCaxCu24O41+σ

Crystal structure, electrical resistivity and magnetic susceptibility were studied for a new superconducting complex cuprate, Sr0.4Ca13.6Cu24O41+delta. The crystal structure consists of S=1/2 Heisenberg two leg ladder and I-D chain systems, in which atomic positions are modulated along the c direction. The resistivity decreases with increasing pressure, and superconductivity was observed with the maximum T-c(onset)=13K at 5GPa. From the analysis of the magnetic susceptibility data at ambient pressure using an alternating chain model, we found that AF (anti-ferro) dimers in the 1-D chain are linked by weak AF interaction.