On the superconductor mechanism of [bis(ethylenedithio)tetraselenafuvalene]2GaCl4

The superconductivity of [BETS]2GaCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene, is discussed in terms of electronic structure properties. The critical temperature, Tc, for the organic superconductor is suggested to be determined by the energy splitting between two electronic states with different spatial extent of the orbitals at the Fermi level. The energetically lowest superconducting state has localized orbitals confined in the BETS moieties, whereas the conventionally conducting state has delocalized orbitals along the [BETS]2GaCl4 chains. The calculations suggest that the open-shell singlet state of [BETS]2GaCl4 pairs is the prerequisite of accepting the superconducting Cooper pairs.