Effect of uranium deficiency on normal and superconducting properties in unconventional superconductor UTe$_2$

Abstract

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.

Slow Electronic Dynamics in the Paramagnetic State of UTe$_2$

“…The observed NMR line broadening below T H would be attributed to spatially distributed spin susceptibility induced by disturbing the long-range FM correlations with tiny amount of disorder or defects within the ladder. 25,43) On the other hand, however, we can not exclude the possibility that the slow fluctuations might occur in charge channel, if the system would be located near an electronic phase boundary. 26) It is expected that the fluctuations of the charge or the electron density at the Fermi energy cause the timedependent modulations of the hyperfine coupling strength between U spins and Te nuclei, leading to the slow fluctuations of the h (t).…”