| Popis: |
We report a study of U{sub 1{minus}{ital x}M{ital x}}Be{sub 13} (0{le}{ital x}{le}0.995 with the nonmagnetic {ital M}=Hf, Zr, Sc, Lu, Y, Pr, Ce, Th, and La), with characterization by x-ray diffraction, resistivity, dc susceptibility, and specific heat. Hybridization, and the distance, between the U 5{ital f} electrons and the Be {ital s} and {ital p} electrons is found to control the specific heat {gamma} and therefore the effective mass {ital m}{sup *}, while the outer electronic configuration of {ital M} plays no role. When the UBe{sub 13} lattice is not expanded by the dopant {ital M}, {gamma} (normalized per U mole) reaches a constant value for {ital x}{gt}0.15 that is about 40% that of pure UBe{sub 13}. This dilute single-ion behavior is also observed in the resistivity. Surprisingly, the low-temperature magnetic susceptibility (normalized per U mole) is independent of doping for all {ital x}. Thus, the large magnetic susceptibility at low temperature in UBe{sub 13} is entirely attributable to single-ion effects. The source of the remaining 60% of the large {ital m}{sup *} in UBe{sub 13} and the implications for heavy-fermion superconductivity are discussed. |
