Superconducting gap structure and thermodynamic phase diagram of (TMTSF)2ClO4 determined by field-angle-resolved calorimetry.
Shingo Yonezawa Department of Physics, Graduate School of Science, Kyoto University
It was in 1980 when the first organic superconductor tetramethyl-tetraselena-fulvalene (TMTSF) salt was discovered by the Orsay group. Because (TMTSF)2X family is an archetypal quasi-one-dimensional (Q1D) conductor with strong electron-electron interaction, it has been providing opportunities to study unique superconducting (SC) phenomena originating from low dimensionality and to investigate generic relation between superconductivity and electron correlation. However, fundamental information such as the SC symmetry, gap structure, and thermodynamic phase diagram remain unclear. To tackle this issue, we developed a calorimeter sensitive enough for a sub-100-micro-gram single crystal of (TMTSF)2ClO4. With this calorimeter, we performed comprehensive field-angle-resolved calorimetry and obtained definitive evidence for a spin-singlet superconductivity with line nodes on the SC gap, as well as the thermodynamic phase diagrams for all principal field directions. Furthermore, we succeeded in the mapping of the SC-gap nodal positions based on the observation of the field-angle dependent quasiparticle excitation for the first time in Q1D superconductors. In this seminar, I describe details of our field-angle-resolved calorimetry. I will show our recent results on the normal-state properties including electronic "nematicity" as well as on the superconducting gap symmetry in high-quality single crystals of BaFe2(As1-xPx)2.