Comparison of the normal state properties of   $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ and its deuterated analogue in high   magnetic fields and under high hydrostatic pressures
  Details of the Fermi-surface topology of deuterated $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ ~have been measured as a function of pressure, and compared with equivalent measurements of the undeuterated salt. We find that the superconducting transition temperature is much more dramatically suppressed by increasing pressure in the deuterated salt. It is suggested that this is linked to pressure-induced changes in the Fermi-surface topology, which occur more rapidly in the deuterated salt than in the undeuterated salt as the pressure is raised. Our data suggest that the negative isotope effect observed on deuteration is due to small differences in Fermi-surface topology caused by the isotopic substitution. 
Tim Biggs, Anne-Katrin Klehe, John Singleton, David Bakker, Jane   Symington, Paul Goddard, Arzhang Ardavan, William Hayes, ...