Superconductivity of highly disperse beryllium films

Peculiarities of the annealing-induced changes in superconducting and electrical properties of ultrathin cold-deposited beryllium films of various thickness (1–5 nm) indicate that the superconducting layers are in metastable fine-crystalline modification which is stabilized by small (< 3 nm) crystallites. The limiting disordering of the metastable phase structure (amorphous state) is incompatible with superconductivity. With the removal of the disorder, superconductivity is observed and enhanced in the impurity-free layers, while the amorphization in the presence of impurities leads to an irreversible suppression of superconductivity. The highest critical temperature Tc = 10.5 K corresponds to the freshly deposited beryllium film of more than 15 nm thickness in which the structure disorder is removed to a considerable extent. The analysis of the data on structural and electrophysical properties of highly disperse films of beryllium and beryllium-based alloys suggests that superconducting phase is a cubic modification of Be (most probably, the β-Be phase).

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