Upper critical field divergence induced by mesoscopic phase separation in the organic superconductor(TMTSF)2ReO4

Abstract

Due to the competition of two anion orders,(TMTSF)2ReO4 presents a phase coexistence between semiconducting and metallic(superconducting) regions (filaments or droplets) in a wide range ofpressures. In this regime, the superconducting upper critical field forH parallelto both c* and b′ axes presents a linear part at low fields followed by a divergence above a crossoverfield. This crossover corresponds to the 3D–2D decoupling transition expected infilamentary or granular superconductors. The sharpness of the transition alsodemonstrates that all filaments are of similar sizes and self-organize in a veryordered way. The distance between the filaments and their cross sections areestimated.