Positron lifetimes in TTF-TCNQ and κ-(BEDT-TTF)2Cu(NCS)2 single crystals

Positron lifetimes in TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) and κ-(BEDT-TTF)2Cu(SCN)2 (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene) single crystals have been measured utilizing a pulsed variable-energy positron beam. The bulk positron lifetimes are 338 and 357 ps, respectively. The incident positron energy dependence of the lifetime is rather weak for both materials. Theoretical simulations have been also performed with several descriptions of the electronic wave functions and the electron-positron correlation. Results are compared with each other and the experiments.