2014 Nous avons effectué des mesures de la chaleur spécifique du supraconducteur organique (TMTSF)2ClO4 entre 0,4 et 2 K. La forte anomalie de la contribution électronique à la chaleur spécifique observée à 1,22 K a été attribuée à l'établissement de l'ordre supraconducteur tridimensionnel. En outre la très forte dépendance de la contribution électronique en champ magnétique au-dessus de 1,22 K n'est pas caractéristique d'un conducteur usuel dans un état normal. Un champ magnétique de 63 kOe appliqué suivant l'axe c* des monocristaux stabilise un état fondamental du système présentant une très faible valeur de la densité d'états au niveau de Fermi (un état soit semiconducteur à petit « gap » soit semimétallique). On observe sous champ une transition isolantconducteur vers 1,4 K. Nos résultats expérimentaux sont bien en accord avec l'existence d'un large domaine fluctuatif supraconducteur unidimensionnel. Abstract. 2014 The specific heat of the organic superconductor (TMTSF)2ClO4 has been measured between 0.4 and 2 K. A large anomaly of the electronic contribution at 1.22 K has been attributed to the onset of three-dimensional superconducting order. There is a large magnetic field dependence of the electronic contribution above 1.22 K which is not characteristic of a normal conducting state. The application of a magnetic field of 63 kOe along the c*-axis of the single crystals restores a ground state exhibiting a very low density of states at the Fermi level (a narrow gap semiconducting or a semimetallic state). A phase transition towards a conducting state with a finite density of states at Fermi level is visible around 1.4 K. Our specific heat results support the existence of a wide 1-D superconducting fluctuating regime.

The low-temperature specific heat of copper-zirconium alloys in both the amorphous and crystalline states has been measured in the whole concentration range where the amorphous state can be reached by melt spinning. The effects of disorder on the electronic, superconducting, and elastic properties are analyzed in the framework of a simple tight-binding model. In spite of the strong reduction of the electron-phonon interaction associated with disorder, superconductivity occurs in some of the amorphous alloys, but in none of the crystalline ones. In the latter the density of states (DOS} at the Fermi level is markedly affected by the particular characteristics of each compound. This is not the case in the amorphous state where the DOS at the Fermi level varies linearly with concentration. In general, we observe in the amorphous state a 30% reduction of the Debye temperature compared to the crystalline compounds. Such a change is dominated by the shear modulus decreasing and cannot be explained by a mean-field model.