Effect of uranium deficiency on normal and superconducting properties in unconventional superconductor UTe 2 .

Single crystals of the unconventional superconductor UTe 2 have been grown in various conditions which result in different superconducting transition temperature as well as normal state properties. Stoichiometry of the samples has been characterized by the single-crystal x-ray crystallography and electron microprobe analyses. Superconducting samples are nearly stoichiometric within an experimental error of about 1%, while non-superconducting sample significantly deviates from the ideal composition. The superconducting UTe 2 showed that the large density of states was partially gapped in the normal state, while the non-superconducting sample is characterized by the relatively large electronic specific heat as reported previously.