Observation of a Non-Magnetic Impurity Effect in the Organic Superconductor (TMTSF)2ClO4

We report a non-magnetic impurity effect on the superconductivity observed in (TMTSF)2ClO4. By varying the sample cooling rate in the vicinity of an anion ordering transition at TAO = 24 K, we can systematically control the amount of disorder in the sample. We then use dc transport and microwave periodic orbit resonance measurements (closely related to cyclotron resonance) to determine the critical temperature Tc and the transport scattering time τ. We find a simple relationship between the two quantities, which strongly suggests that the superconductivity is suppressed by non-magnetic impurities, thus supporting the scenario for unconventional p-wave superconductivity in this material.