Measurement of the energy gap in an organic superconductor: Evidence for extremely strong coupling

Point-contact tunneling is used to make what we believe to be the first measurement of a superconducting energy gap in an organic superconductor. For a -[bis(ethylenedithio)tetrathiafulvalene]2AuI2 single crystal, shows consistent field and temperature dependences, but is more than 4 times larger than weak-coupling BCS value, implying extremely strong coupling. We speculate that very low-frequency modes may be responsible. © 1986 The American Physical Society.