Superconducting Meissner effect under hydrostatic pressure in the ambient-pressure semiconductor κ-(BEDT-TTF)2Cu(N(CN)2)Cl, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene

The known pressure-induced superconductivity in single crystals of κ-(BEDT-TTF${)}_2$Cu(N(CN${)}_2$)Cl where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene has been investigated by static measurements of the diamagnetic shielding and Meissner magnetizations. It is of special interest, since according to previous resistivity measurements, the transition occurs directly from a semiconducting to a superconducting state. The first traces of diamagnetism are observed at a pressure of 80 bars. Both its magnitude and its transition temperature first increase monotonically with pressure, then increase abruptly (between 150 and 200 bars) to develop into a shielding signal of 75% of its ideal value, with a Meissner effect of 25%. At still higher pressures the magnitude of both Meissner and shielding signals becomes pressure independent, while ${\mathit{T}}_{\mathit{c}}$, after reaching a maximum near 13 K, decreases in a fashion similar to related organic superconductors.