| 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. |
- 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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| 3. |
- Heathman, S, et al.
(författare)
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Experimental and ab initio volume compressibility curves of NpCoGa5
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:2, s. 024106-
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of high-pressure, angular-dispersive, x-ray diffraction measurements performed on NpCoGa5, a magnetic isostructural analog of the PuCoGa5 superconductor. No crystallographic transitions or discontinuous volume collapses have been observed by increasing pressure p up to 39 GPa. A fit to the Birch-Murnaghan equation of state gives values of the isothermal bulk modulus and its pressure derivative B-0=130 GPa and B-0'=4.8, respectively. The volume compressibility curve is in excellent agreement with the results of ab initio fully relativistic, full potential local spin-density-functional calculations. A comparison to experimental and ab initio calculated compressibility data of PuCoGa5 and PuRhGa5 is also made.
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| 4. |
- Hen, A., et al.
(författare)
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Structural investigation of Np2Co17 and analogue compounds under pressure
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:5, s. 054107-
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Tidskriftsartikel (refereegranskat)abstract
- The structural behavior of Np2Co17 is investigated by means of high-pressure diamond-anvil compression measurements and is compared with that of the isostructural compounds Lu2Co17 and Lu2Ni17. The Th2Ni17-type hexagonal crystal structure is preserved with no measurable discontinuous volume collapses up to the highest achieved pressure, p = 43 GPa. For Np2Co17, fits to the Birch-Murnaghan and Vinet equations of state give values of the isothermal bulk modulus and its pressure derivative of B-0 = 286 GPa and B-0' = 3, revealing that this Np compound is a highly incompressible solid with stiffness comparable to that of superhard covalently bonded materials. For the Lu2T17 (T = Co, Ni) compounds, the measured bulk modulus changes from B-0 = 137 GPa for T = Co to B-0 = 257 GPa for T = Ni. The isothermal equation of state for the studied compounds are in excellent agreement with the results of ab initio fully relativistic, full-potential local spin-density functional calculations. Theoretical estimates of the bulk modulus are given also for Np2Ni17, for which B-0 is predicted to assume values intermediate between those measured for Lu2Ni17 and Np2Co17.
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| 5. |
- Elgazzar, S., et al.
(författare)
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Electronic structure and Fermi surface of paramagnetic and antiferromagnetic UPt2Si2
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:7, s. 075104-
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Tidskriftsartikel (refereegranskat)abstract
- We report density functional theory-based calculations of the electronic structure and Fermi surface properties of the intermetallic uranium compound UPt2Si2, which orders antiferromagnetically at TN=32 K with a total magnetic moment of 2μB/U-atom and exhibits a moderate mass enhancement in the specific-heat coefficient. Our investigation is carried out using relativistic, full-potential band-structure methods within the framework of the local spin density approximation (LSDA), the LSDA with orbital polarization correction (LSDA+OPC), and the LSDA supplemented with an additional Hubbard U (LSDA+U). We find that the LSDA+OPC scheme predicts the total magnetic moment in best agreement with experiment; from this we infer that the 5f electrons in UPt2Si2 are orbitally polarized, mostly itinerant, and exhibit only a slight tendency toward localization. Our total energy calculations predict UPt2Si2 to form in the CaBe2Si2 (P4/nmm) structure, in contrast to URu2Si2 (ThCr2Si2: I4/mmm). The theoretical Fermi surfaces are also studied for the nonmagnetic and antiferromagnetic phases with the employed computational schemes and are found to be quasi-two-dimensional. At the antiferromagnetic transition, the Fermi surface is found to become more two-dimensional with small regions of gapping.
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| 6. |
- Elgazzar, S., et al.
(författare)
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Electronic structure and Fermi surface of PrMIn5 (M = Co, Rh, and Ir) compounds
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:12, s. 125105-
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Tidskriftsartikel (refereegranskat)abstract
- We report density functional calculations of the electronic structure, Fermi surface, and de Haas-van Alphen (dHvA) quantities of the PrMIn5 (M=Co, Rh, and Ir) compounds. Our investigation is carried out within the framework of the local density approximation, using a relativistic, full-potential band-structure method. A critical analysis of the electronic structures and the de Haas-van Alphen quantities is performed, which shows that good agreement with recent measurements is obtained when we assume the Pr 4f states to be localized. The topology of the Fermi surface is calculated to be similar to that of non-4f reference compounds, e.g., LaRhIn5. The similarities of the Fermi surfaces and the dHvA extremal orbits among the compounds in the series are discussed. We, furthermore, compare our calculated effective masses with experimental measurements and discuss the differences between them.
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| 7. |
- Elgazzar, S, et al.
(författare)
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Hidden order in URu2Si2 originates from Fermi surface gapping induced by dynamic symmetry breaking
- 2009
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Ingår i: Nature Materials. - 1476-1122 .- 1476-4660. ; 8:4, s. 337-341
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Tidskriftsartikel (refereegranskat)abstract
- Spontaneous, collective ordering of electronic degrees of freedom leads to second-order phase transitions that are characterized by an order parameter driving the transition. The notion of a 'hidden order' has recently been used for a variety of materials where a clear phase transition occurs without a known order parameter. The prototype example is the heavy-fermion compound URu2Si2, where a mysterious hidden-order transition occurs at 17.5 K. For more than twenty years this system has been studied theoretically and experimentally without a firm grasp of the underlying physics. Here, we provide a microscopic explanation of the hidden order using density-functional theory calculations. We identify the Fermi surface 'hot spots' where degeneracy induces a Fermi surface instability and quantify how symmetry breaking lifts the degeneracy, causing a surprisingly large Fermi surface gapping. As the mechanism for the hidden order, we deduce spontaneous symmetry breaking through a dynamic mode of antiferromagnetic moment excitations.
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| 8. |
- Opahle, I., et al.
(författare)
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Calculated de Haas-van Alphen frequencies of NpCoGa5
- 2006
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Ingår i: EUROPHYSICS LETTERS. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 74:1, s. 124-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and magnetic properties of NpCoGa5 are investigated in the framework of relativistic density functional theory in the local spin density approximation (LSDA) with and without orbital polarization (OP) corrections. A detailed analysis of the Fermi surface is presented. Comparison of the calculated angular dependence of the de Haas-van Alphen frequencies with recent experimental data shows that LSDA reproduces the main features of the Fermi surface topology, while the spin and orbital moments of NpCoGa5 are less well described. The inclusion of OP corrections leads to a very good agreement between calculated and measured de Haas-van Alphen frequencies, but does not yield a significant improvement of the calculated magnetic properties. We predict that NpCoGa5 shows an intrinsic GMR effect at moderate magnetic field.
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| 9. |
- Oppeneer, Peter, et al.
(författare)
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Fermi surface changes due to localized-delocalized f-state transitions in Ce-115 and Pu-115 compounds
- 2007
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 310:2, s. 1684-1690
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Tidskriftsartikel (refereegranskat)abstract
- The current theoretical understanding of the electronic structures of the CeMIn5 compounds (with M = Co, Rh, and Ir) and PuCoGa5 and PuRhGa5 is reviewed. Both the Ce-115 and Pu-115 compounds have in common that their f-electrons appear to be poised on the edge of a localization-delocalization boundary. We consider here the implications of this characteristic on the emergent electronic structure, addressing, in particular, the computed Fermi surfaces. In order to capture the electronic structures to the best as possible, we employ three different density-functional theory based computational approaches, viz. the local-spin density approximation (LSDA) for delocalized f-states, the open-core approach for localized f's, and the LSDA + U approach for moderately localized f's. The Fermi surfaces of CeCoIn5 and CeIrIn5 are rather well described assuming delocalized 4f electrons. Conversely, the better description is obtained for CeRhIn5 assuming a localized 4f state. For the Pu-115 compounds, LSDA calculations predict a rather two-dimensional Fermi surface. However, the Fermi surface of PuCoGa5 computed with the around-mean field LSDA + U scheme is also quite two-dimensional and, moreover, similar to the LSDA Fermi surface. Taking other available experimental data on PuCoGa5 into account, it appears that the electronic structure of PuCoGa5 is best described by the AMF-LSDA + U approach with a Coulomb U of about 3 eV.
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| 10. |
- Oppeneer, Peter M., et al.
(författare)
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Spin and orbital hybridization at specifically nested Fermi surfaces in URu(2)Si(2)
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:24, s. 241102-
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Tidskriftsartikel (refereegranskat)abstract
- The Fermi-surface (FS) nesting properties of URu(2)Si(2) are analyzed with particular focus on their implication for the mysterious hidden order phase. We show that there exist two Fermi surfaces that exhibit a strong nesting at the antiferromagnetic wave vector Q(0) = (0,0,1). The corresponding energy dispersions fulfill the relation epsilon(1)(k) = -epsilon(2)(k +/- Q(0)) at eight FS hot-spot lines. The spin-orbital characters of the involved 5f states are distinct (j(z) = +/-5/2 vs +/-3/2) and hence the degenerate Dirac crossings are symmetry protected in the nonmagnetic normal state. Dynamical symmetry breaking through an Ising-like spin and orbital excitation mode with Delta j(z) = +/-1 induces a hybridization of the two states, causing substantial FS gapping. Concomitant spin and orbital currents in the uranium planes give rise to a rotational symmetry breaking.
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