Theory of a uranium impurity in metals fluctuating between two magnetic configurations

Nunes, André; Rasul, J.W.; Gehring, G A

doi:10.1088/0022-3719/19/7/013

Cited by 22 publications

(6 citation statements)

References 22 publications

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“…A logarithmic T -dependence with a negative slope of ρ(T ) was also reported for Th 0.86 U 0.14 Sb [20]. Again, the situation seems ambiguous and a mixture of mixed-valency and Kondo effect cannot be excluded [21]. Our data, however, indicate that the insertion of U at the low at.…”

supporting

confidence: 76%

“…A logarithmic T -dependence with a negative slope of ρ(T ) was also reported for Th 0.86 U 0.14 Sb [21]. Again, the situation seems ambiguous and a mixture of mixed valency and Kondo effect cannot be excluded [22]. Our data, however, indicate that the insertion of U at the low at.% level into a matrix with a very low conduction electron concentration, such as CaB 6 , favors the stability of the local moment on the U site, leading to a well-developed classical Kondo effect at low temperatures.…”

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confidence: 56%

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Kondo behavior of U in CaB ₆

et al. 2004

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Replacing U for Ca in semiconducting CaB6 at the few at.% level induces metallic behaviour and Kondo-type phenomena at low temperatures, a rather unusual feature for U impurities in metallic hosts. For Ca0.992U0.008B6, the resistance minimum occurs at T = 17 K. The subsequent characteristic logarithmic increase of the resistivity with decreasing temperature merges into the expected T 2-dependence below 0.8 K. Data of the low-temperature specific heat and the magnetization are analyzed by employing a simple resonance-level model. Analogous measurements on LaB6 with a small amount of U revealed no traces of Kondo behavior, above 0.4 K.

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confidence: 76%

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confidence: 56%

Kondo behavior of U in CaB ₆

et al. 2004

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“…A 1 /N scheme that gave the same results at zero temperature was developed to leading order by Read et al [15]. The same low energy scale was found in a variational study of the f&-f' Anderson mode by Nunes et al [16]. Other bulk properties have been discussed within this scheme [17].…”

Section: Low Temperature Properties Of the Two Magnetic State Andersomentioning

confidence: 75%

Local and band approaches to actinide systems

Rasul

1991

Physica B: Condensed Matter

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Invited papel We investigate two models of interest in the context of actinide and rare earth systems. We extend previous work on the Anderson model for two magnetic configurations and obtain the singlet quasiparticle energy to next leading order in the 1 i N expansion. We prove that the appropriate Ward identity and perturbative scaling results are reproduced in this theory. We also prove the opposite limit in which there is significant f-f overlap using the infinite U Hubbard model. Working to second order in the l/N expansion, we study the quasiparticle scattering amplitudes and find a large enhancement in the Landau parameter f: near half filling which varies as the cube of the mass enhancement. For a free-electron-like dispersion relation, this implies a transition to a ferromagnetic state for small hole concentrations.

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“…However, the impurity Anderson model seems to be rife with theoretical surprises. In the only theoretical work to date on the interplay of spin and charge fluctuations, addressed specifically at uranium, Rasul and coworkers have found [34][35][36] numerically in an inverse degeneracy treatment that the impurity Anderson Hamiltonian with fluctuating valence between f 2 and f 3 can have a small energy scale even for nf near 2.5. This treatment did not include multiplet splittings.…”

Section: Uranium Materials-relation Of Thermodynamics and Spectroscopymentioning

confidence: 99%