HIGH-PRESSURE TRANSPORT-PROPERTIES OF THE SUPERCONDUCTING SPIN-LADDERSYSTEM SR14-XCAXCU24O41+DELTA

We report the electrical resistivity, the Hall coefficient, Rw, and th e magnetoresistance, MR, at pressures up to 2.0 GPa, of the spin-ladde r compound Sr14-xCaxCu24O41+delta, on both a polycrystal (x = 13.6) an d single crystals (x = 11 and 12), in which superconductivity has been observed only in a range of both Ca content (similar to 11 < x < 14) and pressure (similar to 1.5 < P < similar to 8 GPa). The pressure dep endence of the R-H, with positive sign, indicates that carrier density increases with increasing pressure and localization of hole carriers at low temperature is substantially suppressed by applying pressure. W e have also found that a positive MR, which violates Kohler's rule, se ems to appear below the temperature at which a spin gap begins to open and strongly depends on the temperature as well as both on Ca content and applied pressure, suggesting that this MR is closely related to t he mobile holes in the spin singlet state.