Superconductivity and pseudogap states in λ-(BEDT-TSF)2GaCl4:: Microwave conductivity measurements

We have investigated the 45 GHz microwave response from an organic superconductor lambda-(BEDT-TSF)(2)GaCl4 with T-c = 4.8 K. In the superconducting state, the London penetration depth saturates well below T-c, which may provide an evidence for a conventional s-wave paring. In the metallic state, sigma(c)(1) deviates downward from sigma(c)(dc), while sigma(c)(2), which should be zero in a conventional metallic state, increases exponentially toward T,. This anomalous metallic state has been discussed in terms of a possible formation of incoherent electron pairs in so-called a pseudogap state.