Re(-u lo 19 dt,(-embre 1979, aocopto l0 3 janvier 1980) Résumé. 2014 Nous avons observé le phénomène de supraconductibilité dans le conducteur organique quasi-unidimensionnel di-(tétraméthyltétraselénofulvalène)-hexafluorophosphate, (TMTSF)2PF6, par mesures résistives sous pression hydrostatique de 12 kbar à une température de 0,9 K. Nous présentons aussi l'effet de champs magnétiques perpendiculaires à l'axe des chaines. Abstract. 2014 Superconductivity has been observed by resistive measurements in the quasi-one dimensional organic conductor di-(tetramethyltetraselenafulvalene)-hexafluorophosphate, (TMTSF)2PF6 under a hydrostatic pressure of 12 kbar with a transition temperature of 0.9 K. The effect of magnetic fields perpendicular to the chain axis is also reported.

The thermal conductivity of a YBa 2 Cu 3 O 6.9 detwinned single crystal has been studied as a function of the relative orientation of the crystal axes and a magnetic field rotating in the Cu-O planes. Measurements were carried out at several different temperatures below T c (0.5 K < T< 25 K) and at a fixed field of 30 kOe. A four-fold symmetry characteristic of a superconducting gap with nodes at odd multiples of 45 degrees in k-space was resolved. Experiments were performed to exclude a possible macroscopic origin for such a four-fold symmetry such as sample shape or anisotropic pinning. Our results impose an upper limit of 10% on the weight of the s-wave component of the essentially d-wave superconducting order parameter of YBCO. 74.25.Fy, 74.72.Bk, 72.15.Eb Typeset using REVT E X 1