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Register a new userTemperature Dependent 5f-states in URu_2Si_2
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Added by
Jonathan D. Denlinger
Publication date
2001
fields
Physics
and research's language is
English
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A dramatic temperature dependent enhancement of U 5f spectral weight at $E_F$ is observed in angle-resolved photoemission measurements of $URu_2Si_2$ at the center of an X-point hole-pocket. Comparison of this temperature dependent behavior for excitation both at and below the U $5d to 5f$ resonant threshold is presented.
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We have investigated the electronic states of the uranium monochalcogenide US, which is a typical ferromagnetic uranium compound, using soft x-ray photoemission spectroscopy (SX-PES). In early ultraviolet photoemission spectroscopy studies, two peak structures of the U 5f states were observed and have been interpreted that one has an itinerant character around the Fermi level (EF) and the other located below EF has a character of localized U 5f electrons. In this study, the intrinsic bulk valence-band spectrum of US was first deduced by estimating the contribution of surface states to the valence-band spectrum using core-level photoemission spectra. We conclude that the electronic structure of US can be basically described by the itinerant nature of the U 5f electrons from comparison with theoretical valence-band spectra obtained by band-structure calculation in the local-density approximation.
Actinide elements produce a plethora of interesting physical behaviors due to the 5f states. This review compiles and analyzes progress in understanding of the electronic and magnetic structure of the 5f states in actinide metals. Particular interest is given to electron energy-loss spectroscopy and many-electron atomic spectral calculations, since there is now an appreciable library of core d -> valence f transitions for Th, U, Np, Pu, Am, and Cm. These results are interwoven and discussed against published experimental data, such as x-ray photoemission and absorption spectroscopy, transport measurements, and electron, x-ray, and neutron diffraction, as well as theoretical results, such as density-functional theory and dynamical mean-field theory.
We present a theoretical model of the electronic structure of delta-Pu that is consistent with many of the electronic structure related properties of this complex metal. In particular we show that the theory is capable of reproducing the valence band photoelectron spectrum of delta-Pu. We report new experimental photoelectron spectra at several photon energies and present evidence that the electronic structure of delta-Pu is unique among the elements, involving a 5f shell with four 5f electrons in a localized multiplet, hybridizing with valence states, and approximately one 5f electron forming a completely delocalized band state.
The temperature-dependent evolution pattern of 5f electrons helps to elucidate the long-standing itinerant-localized dual nature in plutonium-based compounds. In this work, we investigate the correlated electronic states of PuIn3 dependence on temperature by using a combination of the density functional theory and the dynamical mean-field theory. Not only the experimental photoemission spectroscopy is correctly reproduced, but also a possible hidden 5f itinerant-localized crossover is identified. Moreover, it is found that the quasiparticle multiplets from the many-body transitions gradually enhance with decreasing temperature, accompanied by the hybridizations with 5f electrons and conduction bands. The temperature-induced variation of Fermi surface topology suggests a possible electronic Lifshitz transition and the onset of magnetic order at low temperature. Finally, the ubiquitous existence orbital selective 5f electron correlation is also discovered in PuIn3. These illuminating results shall enrich the understanding on Pu-based compounds and serve as critical predictions for ongoing experimental research.
We have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial $mathrm{U}~5f$ density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the $mathrm{U}~4d-5f$ resonant photoemission spectroscopy. Obtained $mathrm{U}~5f$ pDOS exhibit a systematic trend depending on the physical properties of compounds. The coherent peak at the Fermi level can be described by the band-structure calculation, but an incoherent peak emerges on the higher binding energy side ($lesssim 1~mathrm{eV}$) in the Uf pDOS of localized and heavy fermion compounds. As the $mathrm{U}~5f$ state is more localized, the intensity of the incoherent peak is enhanced and its energy position is shifted to higher binding energy. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard-$U$ type mechanism takes an essential role in the $5f$ electronic structure of actinide materials.
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