Muon spin rotation study of the (TMTSF)2ClO4 system

We report a study of the organic compound (TMTSF)2ClO4 in both a sample cooled very slowly through the anion ordering temperature (relaxed state) and a sample cooled more rapidly (intermediate state). For the relaxed state the entire sample is observed to be superconducting below about Tc≃1.2 K. The second moment of the internal field distribution was measured for the relaxed state yielding an in-plane penetration depth of ≃12000 Å. The intermediate state sample entered a mixed phase state, characterized by coexisting macroscopic sized regions of superconducting and spin density wave (SDW) regions, below Tc≃0.87 K. These data were analyzed using a back-to-back cutoff exponential function, allowing the extraction of the first three moments of the magnetic field distribution. Formation of a vortex lattice is observed below 0.87 K as evidenced by the diamagnetic shift for the two fields in which we took intermediate state data.