On the 'inverse' isotope effect in organic superconductors: new findings and implications

摘要

The "inverse" deuterium isotope effect, previously found in #kappa#-(BEDT-TTF)_2Cu(NCS)_2, is also found in two other BEDT-TTF based superconductors with different packing motifs and different types of anions. Remarkably, the magnitude of the isotope shift is essentially identical in all three superconductors, ca. +0.26+-0.06 K. These results, when taken together with the recent results of Lang et al. on the uniaxial pressure derivatives of T_c, suggest that the "inverse" isotope effect may not have a direct relationship to the pairing mechanism but instead is a reflection of the change in the "internal lattice pressure".