Pressure-Induced Dimensional Crossover and Superconductivity in the Hole-Doped Two-Leg Ladder Compound Sr14-xCaxCu24O41

Anisotropic electrical resistivity under high pressure was measured for a single crystal of ${\mathrm{Sr}}_{2.5}{\mathrm{Ca}}_{11.5}-{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$, a hole-doped two-leg ladder compound. Superconductivity was observed between 3.5 and 8 GPa, accompanied by metallic resistivity between the ladders, which indicates semiconducting behavior at ambient pressure. This in turn strongly suggests that the application of pressure brings about a dimensional crossover from one to two, and that superconductivity in this system is a consequence of an insulator to superconductor transition in the anisotropic two-dimensional system.