A Possible Mechanism of the Pseudogap in Organic Superconductor Based on the Superconducting Fluctuation

The explanation of the anomalous behavior in $\kappa$-type (BEDT-TTF)${}_2$X which was revealed by the nuclear magnetic resonance experiments is presented. We calculate the electronic properties by using the one-loop approximation for the superconducting fluctuation. The decrease of the density of states due to the large damping effect is obtained and the one-particle spectrum has a pseudogap structure around the Fermi level. It is found that these behaviors are peculiar to the quasi two-dimensional system and are enhanced in the incoherent metal. The similarity between the cuprates and this compounds is discussed and an experiment to check this proposal is suggested.