Electronic properties of γ-U and superconductivity of U–Mo alloys

• The bcc phase of uranium was stabilized to low temperature in U–Mo alloys.
• Ultrafast cooling was utilized.
• Negative coefficient dρ/dT indicates very strong disorder.
• The alloys are superconducting with Tc ≈ 2.1 K.
• They exhibit high critical field exceeding 5 T.

Fundamental electronic properties of γ-Uranium were determined using Mo doping combined with ultrafast (splat) cooling, which allowed stabilization of the bcc structure to low temperatures. The Sommerfeld coefficient γe is enhanced to 16 mJ/mol K2 from 11 mJ/mol K2 for α-U. Magnetic susceptibility remains weak and T-independent, ≈5 × 10−8 m3/mol. The Mo-doped γ-U exhibits a conventional BCS superconductivity with Tc ≈ 2.1 K and critical field exceeding 5 T for 15 at.% Mo. This type of superconductivity is qualitatively different from the one found for pure U splat, which has Tc higher than 1 K but the weak specific heat anomaly proves that it is not real bulk effect.