We report measurements of the de Haas–van Alphen (DHVA) effect and ac susceptibility in the layered organic superconductor $\kappa -(\mathrm{BEDT}-\mathrm{TTF}{)}_2\mathrm{Cu}(\mathrm{NCS}{)}_2.$ The amplitude of the DHVA oscillations is attenuated over a wide field range above the irreversibility line, $B_{\mathrm{irr}}\mathrm{}\left(B\right),$ below which a rigid flux lattice is formed. Thus the DHVA effect provides a unique probe of the superconducting fluctuations at high fields in this material. We compare our measurements with other measurements of the superconducting phase diagram of $\kappa -(\mathrm{BEDT}-\mathrm{TTF}{)}_2\mathrm{Cu}(\mathrm{NCS}{)}_2.$

• Received 5 July 2001

DOI:https://doi.org/10.1103/PhysRevB.65.064515