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An Alternative Model for Electron Correlation in Pu

Description: Using a density functional theory based approach that treats the 5f electrons relativistically, a Pu electronic structure with zero net magnetic moment is obtained, where the 5f orbital and 5f spin moments cancel each other. By combining the spin and orbital specific densities of states with state, spin and polarization specific transition moments, it is possible to reconstruct the experimentally observed photoemission spectra from Pu. Extrapolating to a spin-resolving Fano configuration, it is shown how this would resolve the extant controversy over Pu electronic structure.
Date: October 23, 2007
Creator: Yu, S; Tobin, J & Soderlind, P
Partner: UNT Libraries Government Documents Department

Evidence for the Spectroscopic Signature of Aging in (delta)-Pu(Ga)

Description: Plutonium, because of its radioactive nature, ages from the 'inside out' by means of self-irradiation damage and thus produces nanoscale internal defects. The self-irradiation induced defects come in the form of Frenkel-type defects (vacancies and self-interstitial atoms), helium in-growth, and defect clusters. At present there are neither experimental nor theoretical models describing the changes in the electronic structure caused by the aging in Pu. This fact appears to be associated primarily with the absence of reasonably convincing spectroscopic evidence of the changes. This paper demonstrates that Resonant Photoemission, a variant of Photoelectron Spectroscopy, has strong sensitivity to aging of Pu samples. The spectroscopic results are correlated with an extra-atomic screening model [1], and are shown to be the fingerprint of mesoscopic or nanoscale internal damage in the Pu physical structure. This means that a spectroscopic signature of internal damage due to aging in Pu has been established.
Date: November 23, 2005
Creator: Chung, B W; Schwartz, A J; Ebbinghaus, B B; Fluss, M J; Haslam, J J; Blobaum, K M et al.
Partner: UNT Libraries Government Documents Department

Cancellation of spin and orbital magnetic moments in (delta)-Pu: theory

Description: Density functional theory (DFT), in conjunction with the fixed-spin-moment (FSM) method, spin-orbit coupling (SO), and orbital polarization (OP), is shown to retain key features of the conventional DFT treatment of {delta}-Pu while at the same time not producing the substantial net magnetic moments commonly predicted by this theory. It is shown that when a small adjustment of the spin moment (less than 20%) is allowed, a complete spin- and orbital-moment cancellation occurs which results in a zero net magnetic moment in {delta}-Pu. This minor modification, accomplished by the FSM method, is shown to have a very small effect on the calculated total energy as well as the electron density-of-states (DOS). The photoemission spectra (PES), obtained from the DOS of the present model, compares equal or better to measured spectra, than that of two other recent non-magnetic models for {delta}-Pu.
Date: June 23, 2006
Creator: Soderlind, P
Partner: UNT Libraries Government Documents Department

ARPES Studies of Cuprate Fermiology: Superconductivity, Pseudogap and Quasiparticle Dynamics

Description: We present angle-resolved photoemission spectroscopy (ARPES) studies of the cuprate high-temperature superconductors which elucidate the relation between superconductivity and the pseudogap and highlight low-energy quasiparticle dynamics in the superconducting state. Our experiments suggest that the pseudogap and superconducting gap represent distinct states, which coexist below T{sub c}. Studies on Bi-2212 demonstrate that the near-nodal and near-antinodal regions behave differently as a function of temperature and doping, implying that different orders dominate in different momentum-space regions. However, the ubiquity of sharp quasiparticles all around the Fermi surface in Bi-2212 indicates that superconductivity extends into the momentum-space region dominated by the pseudogap, revealing subtlety in this dichotomy. In Bi-2201, the temperature dependence of antinodal spectra reveals particle-hole asymmetry and anomalous spectral broadening, which may constrain the explanation for the pseudogap. Recognizing that electron-boson coupling is an important aspect of cuprate physics, we close with a discussion of the multiple 'kinks' in the nodal dispersion. Understanding these may be important to establishing which excitations are important to superconductivity.
Date: June 23, 2011
Creator: Vishik, Inna
Partner: UNT Libraries Government Documents Department


Description: High resolution angle-resolved photoemission spectroscopy of highly overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} with a T{sub c} = 51K indicates that the basic transport processes in this material are fundamentally different from both the lesser doped cuprates as well as model metallic compounds. The overdoped sample has sharp ARPES peaks at the Fermi energy throughout the Brillouin zone even in the normal state, unlike the lesser-doped compounds. In particular, the spectra near ({pi},0) point show the presence of a sharp peak well above T{sub c}. The ARPES lineshapes, and thus the self energy, at a given energy are almost independent of k. Further, the quasiparticle scattering rate at the Fermi energy seems to be closely tied to direct resistivity measurements. This leads us to the conclusion that overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} is best described as a quasiparticle liquid. However, the energy dependence of the scattering rates is quite similar to that found in the lesser-doped compounds and quite different from that seen in a typical metal.
Date: July 23, 2001
Partner: UNT Libraries Government Documents Department