| 1. |
- Durakiewicz, T., et al.
(författare)
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Observation of a kink in the dispersion of f-electrons
- 2008
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 84:3, s. 37003-
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Tidskriftsartikel (refereegranskat)abstract
- Strong interactions in correlated electron systems may result in the formation of heavy quasiparticles that exhibit kinks in their dispersion relation. Spectral weight is incoherently shifted away from the Fermi energy, but Luttinger's theorem requires the Fermi volume to remain constant. Our angle-resolved photoemission study of USb2 reveals a kink in a noncrossing 5f band, representing the first experimental observation of a kink structure in f-electron systems. The kink energy scale of 21 meV and the ultra-small peak width of 3 meV are observed. We propose the novel mechanism of renormalization of a point-like Fermi surface, and that Luttinger's theorem remains applicable.
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| 2. |
- Song, Jiao-Jiao, et al.
(författare)
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Relocalization of uranium 5f electrons in the antiferromagnetic heavy-fermion superconductor UPd2Al3 : Insights from angle-resolved photoemission spectroscopy
- 2024
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:20
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the antiferromagnetic heavy fermion superconductor UPd2Al3, employing angle-resolved photoemission spectroscopy to unravel the complex electronic structure of its U 5? electrons. We observe unexpected characteristics that challenge the conventional temperature-dependent behavior of heavy fermion systems, revealing unexpected characteristics. At temperatures above the anticipated coherence temperature (?*), we observe itinerant U 5? electrons at temperatures higher than previously postulated. Additionally, a previously unidentified dispersionless band emerges around 600 meV below the Fermi energy, potentially linked to spin-orbit splitting within the U 5? states. Hybridization between the 5? electrons and conduction band was observed with an energy dispersion of 10 meV at low temperatures, suggesting that U 5? electrons near and at the Fermi surface have an itinerant nature. Temperature-dependent 5?−5? resonance spectra reveal that the 5? electron spectrum weight increases with lowering temperature and begins to decrease at temperatures significantly higher than the Néel temperature (??). We further show that the competition between the Kondo effect and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions may be responsible for the relocalization of 5? electrons, making relocalization a precursor to the establishment of magnetic order at lower temperatures. Our experiments also provide evidence that 5? electrons with the same orbital are involved in both the Kondo effect and RKKY interactions, suggesting that the two coexist at lower temperatures.
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| 3. |
- Yang, X, et al.
(författare)
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Unusual quasiparticle renormalizations from angle resolved photoemission on USb2
- 2009
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Ingår i: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 89:22-24, s. 1893-1911
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoemission experiments have been performed on USb2, and very narrow quasiparticle peaks have been observed in a band, which local spin-density approximation (LSDA) predicts to osculate the Fermi energy. The observed band is found to be depressed by 17 meV below the Fermi energy. Furthermore, the inferred quasiparticle dispersion relation for this band exhibits a kink at an energy of about 23 meV below the Fermi energy. The kink is not found in LSDA calculations and, therefore, is attributable to a change in the quasiparticle mass renormalization by a factor of approximately 2. The existence of a kink in the quasiparticle dispersion relation of a band that does not cross the Fermi energy is unprecedented. The kink in the quasiparticle dispersion relation is attributed to the effect of the interband self-energy, involving transitions from the osculating band into a band that does cross the Fermi energy.
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| 4. |
- Dakovski, Georgi L., et al.
(författare)
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Anomalous femtosecond quasiparticle dynamics of hidden order state in URu(2)Si(2)
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:16, s. 161103-
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Tidskriftsartikel (refereegranskat)abstract
- At T(0) = 17.5 K an exotic phase emerges from a heavy fermion state in URu(2)Si(2). The nature of this hidden order (HO) phase has so far evaded explanation. Formation of an unknown quasiparticle (QP) structure is believed to be responsible for the massive removal of entropy at the HO transition, however, experiments and ab initio calculations have been unable to reveal the essential character of the QP. Here we use femtosecond pump-probe time-and angle-resolved photoemission spectroscopy (tr-ARPES) to elucidate the ultrafast dynamics of the QP. We show how the Fermi surface is renormalized by shifting states away from the Fermi level at specific locations, characterized by vector q(< 110 >) = 0.56 +/- 0.08 angstrom(-1). Measurements of the temperature-time response reveal that, upon entering the HO, the QP lifetime in those locations increases from 42 fs to few hundred fs. The formation of the long-lived QPs is identified here as a principal actor of the HO.
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| 5. |
- Durakiewicz, T., et al.
(författare)
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Quest for Band Renormalization and Self-Energy in Correlated f-Electron Systems
- 2010
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 117:2, s. 264-267
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Tidskriftsartikel (refereegranskat)abstract
- Coexisting low-energy scales are observed in f-electron materials. The information about some of low-energy scales is imprinted in the electron self-energy, which can be measured by angle-resolved photoemission (ARPES). Such measurements in d-electron materials over the last decade were based on high energy- and momentum-resolution ARPES techniques used to extract the self-energy information from measured spectra. Simultaneously, many-body theoretical approaches have been developed to find a link between the self-energy and many-body interactions. Here we show the transcription of such methods from d-electrons to f-electrons by presenting the first example of low energy scales in the f-electron material USb2, measured with synchrotron-based ARPES. The proposed approach will help in answering the fundamental questions about the complex nature of the heavy fermion state.
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| 6. |
- Meng, Jian-Qiao, et al.
(författare)
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Imaging the Three-Dimensional Fermi-Surface Pairing near the Hidden-Order Transition in URu2Si2 Using Angle-Resolved Photoemission Spectroscopy
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:12, s. 127002-
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Tidskriftsartikel (refereegranskat)abstract
- We report angle-resolved photoemission spectroscopy experiments probing deep into the hidden-order state of URu2Si2, utilizing tunable photon energies with sufficient energy and momentum resolution to detect the near Fermi-surface (FS) behavior. Our results reveal (i) the full itinerancy of the 5f electrons, (ii) the crucial three-dimensional k-space nature of the FS and its critical nesting vectors, in good comparison with density-functional theory calculations, and (iii) the existence of hot-spot lines and pairing of states at the FS, leading to FS gapping in the hidden-order phase.
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| 7. |
- Mydosh, J. A., et al.
(författare)
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Hidden order and beyond : an experimental-theoretical overview of the multifaceted behavior of URu2Si2
- 2020
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 32:14
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Forskningsöversikt (refereegranskat)abstract
- This topical review describes the multitude of unconventional behaviors in the hidden order, heavy fermion, antiferromagnetic and superconducting phases of the intermetallic compound URu2Si2 when tuned with pressure, magnetic field, and substitutions for all three elements. Such 'perturbations' result in a variety of new phases beyond the mysterious hidden order that are only now being slowly understood through a series of state-of-the-science experimentation, along with an array of novel theoretical approaches. Despite all these efforts spanning more than 30 years, hidden order (HO) remains puzzling and non-clarified, and the search continues in 2019 into a fourth decade for its final resolution. Here we attempt to update the present situation of URu2Si2 importing the latest experimental results and theoretical proposals. First, let us consider the pristine compound as a function of temperature and report the recent measurements and models relating to its heavy Fermi liquid crossover, its HO and superconductivity (SC). Recent experiments and theories are surmized that address four-fold symmetry breaking (or nematicity), Isingness and unconventional excitation modes. Second, we review the pressure dependence of URu2Si2 and its transformation to antiferromagnetic long-range order. Next we confront the dramatic high magnetic-field phases requiring fields above 40 T. And finally, we attempt to answer how does random substitutions of other 5f elements for U, and 3d, 4d, and 5d elements for Ru, and even P for Si affect and transform the HO. Commensurately, recent theoretical models are summarized and then related to the intriguing experimental behavior.
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