Electronic structure theory of the hidden order material URu2_2Si2_2

We report a comprehensive electronic structure investigation of the paramagnetic (PM), the large moment antiferromagnetic (LMAF), and the hidden order (HO) phases of URu$_2$Si$_2$. We have performed relativistic full-potential calculations on the basis of the density functional theory (DFT), employing different exchange-correlation functionals to treat electron correlations within the open $5f$-shell of uranium. Specifically, we investigate---through a comparison between calculated and low-temperature experimental properties---whether the $5f$ electrons are localized or delocalized in URu$_2$Si$_2$. We also performed dynamical mean field theory calculations (LDA+DMFT) to investigate the temperature evolution of the quasi-particle states at 100~K and above, unveiling a progressive opening of a quasi-particle gap at the chemical potential when temperature is reduced. A detailed comparison of calculated properties with known experimental data demonstrates that the LSDA and GGA approaches, in which the uranium $5f$ electrons are treated as itinerant, provide an excellent explanation of the available low-temperature experimental data of the PM and LMAF phases. We show furthermore that due to a materials-specific Fermi surface instability a large, but partial, Fermi surface gapping of up to 750 K occurs upon antiferromagnetic symmetry breaking. The occurrence of the HO phase is explained through dynamical symmetry breaking induced by a mode of long-lived antiferromagnetic spin-fluctuations. This dynamical symmetry breaking model explains why the Fermi surface gapping in the HO phase is similar but smaller than that in the LMAF phase and it also explains why the HO and LMAF phases have the same Fermi surfaces yet different order parameters. Suitable derived order parameters for the HO are proposed to be the Fermi surface gap or the dynamic spin-spin correlation function.Comment: 23 pages, 20 figure

Theory for the electromigration wind force in dilute alloys

A multiple scattering formulation for the electromigration wind force on atoms in dilute alloys is developed. The theory describes electromigration via a vacancy mechanism. The method is used to calculate the wind valence for electromigration in various host metals having a close-packed lattice structure, namely aluminum, the noble metals copper, silver and gold and the $4d$ transition metals. The self-electromigration results for aluminum and the noble metals compare well with experimental data. For the $4d$ metals small wind valences are found, which make these metals attractive candidates for the experimental study of the direct valence.Comment: 18 pages LaTeX, epsfig, 8 figures. to appear in Phys. Rev. B 56 of 15/11/199

Efficient metallic spintronic emitters of ultrabroadband terahertz radiation

Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source which relies on tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photo-induced spin currents, the inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an analytical model, such spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and cost.Comment: 18 pages, 10 figure

Probing The Electronic Structure Of Pure And Doped Cem In5 (m=co,rh,ir) Crystals With Nuclear Quadrupolar Resonance

We report calculations of the electric-field gradients (EFGs) in pure and doped CeM In5 (M=Co, Rh, and Ir) compounds and compare with experiment. The degree to which the Ce4f electron is localized is treated within various models: the local-density approximation, generalized gradient approximation (GGA), GGA+U, and 4f -core approaches. We find that there is a correlation between the observed EFG and whether the 4f electron participates in the band formation or not. We also find that the EFG evolves linearly with Sn doping in CeRhIn5, suggesting the electronic structure is modified by doping. In contrast, the observed EFG in CeCoIn5 doped with Cd changes little with doping. These results indicate that nuclear quadrupolar resonance is a sensitive probe of electronic structure. © 2008 The American Physical Society.7724Slichter, C.P., (1990) Principles of Magnetic Resonance, , 3rd ed. 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Magnetic state of plutonium ion in metallic Pu and its compounds

By LDA+U method with spin-orbit coupling (LDA+U+SO) the magnetic state and electronic structure have been investigated for plutonium in \delta and \alpha phases and for Pu compounds: PuN, PuCoGa5, PuRh2, PuSi2, PuTe, and PuSb. For metallic plutonium in both phases in agreement with experiment a nonmagnetic ground state was found with Pu ions in f^6 configuration with zero values of spin, orbital, and total moments. This result is determined by a strong spin-orbit coupling in 5f shell that gives in LDA calculation a pronounced splitting of 5f states on f^{5/2} and f^{7/2} subbands. A Fermi level is in a pseudogap between them, so that f^{5/2} subshell is already nearly completely filled with six electrons before Coulomb correlation effects were taken into account. The competition between spin-orbit coupling and exchange (Hund) interaction (favoring magnetic ground state) in 5f shell is so delicately balanced, that a small increase (less than 15%) of exchange interaction parameter value from J_H=0.48eV obtained in constrain LDA calculation would result in a magnetic ground state with nonzero spin and orbital moment values. For Pu compounds investigated in the present work, predominantly f^6 configuration with nonzero magnetic moments was found in PuCoGa5, PuSi2, and PuTe, while PuN, PuRh2, and PuSb have f^5 configuration with sizeable magnetic moment values. Whereas pure jj coupling scheme was found to be valid for metallic plutonium, intermediate coupling scheme is needed to describe 5f shell in Pu compounds. The results of our calculations show that both spin-orbit coupling and exchange interaction terms in the Hamiltonian must be treated in a general matrix form for Pu and its compounds.Comment: 20 pages, LaTeX; changed discussion on reference pape