Optical response of the ladder compound Sr2.5Ca11.5Cu24O41 under high pressure

Since the discovery of a pressure-induced superconducting phase, the highly Ca-doped Sr14-xCaxCu24O41 two-leg ladder compound is intensively investigated. Based on earlier studies it was suggested that Ca doping as well as the application of pressure transfer holes from the chains to the ladders. The nature of the superconductivity, however, remains an open issue. An important piece of information is how the dynamics of the charge carriers change upon pressure application. We therefore studied the pressure-dependent optical response of Sr2.5Ca11.5Cu24O41 over a broad frequency range (far-infrared to visible) at room temperature. Based on these results, we will discuss the possible occurrence of a pressure-induced dimensional crossover in Sr2.5Ca11.5Cu24O41 and speculate on the implications of our findings for the superconductivity in this system. (orig.)