Chemical Facets of Superconductivity in UTe₂

Understanding superconductivity requires a deep comprehension of the chemical structure. The discovery of a new unconventional superconductor UTe₂ a few years ago prompted many detailed investigations of its physical properties. Despite its unconventional ground state being rather well-studied, a strong sample-to-sample variation of superconducting behavior as a result of different preparation conditions has remained largely unexplained until now. In this work, an in-depth analysis of the UTe₂ crystal structure and resultant physical properties by implementing several types of synthetic routes was carried out. The difference between superconducting and non-superconducting UTe₂ lies in the presence of uranium vacancies, on the order of 4%. As a result, the b and c lattice parameters vary, yielding a volume difference of about 0.51%. A subtler difference between samples exhibiting one and two superconducting transitions is driven by local deviations from the translational symmetry in the main atomic arrangement. Several well-pronounced maxima have been observed in the difference density map, predominantly located in the bc plane due to a local appearance of the similar atomic arrangements in different orientations. The extreme sensitivity of UTe₂ to such a small number of defects re-emphasizes the unconventional nature of superconductivity in this compound. Furthermore, this work underscores the importance of a thorough, combined chemical and physical analysis of intriguing strongly correlated materials─in particular for compounds that are known to exhibit nontrivial ground states and exotic accompanying phenomena.