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Extraordinarily sharp spectral features at binding energies near leV have been observed in the photoemission spectra of untwinned, single crystal YBa2Cu3O6.9. This is the first observation of such distinctive electronic structure away... more
Extraordinarily sharp spectral features at binding energies near leV have been observed in the photoemission spectra of untwinned, single crystal YBa2Cu3O6.9. This is the first observation of such distinctive electronic structure away from the near-Fermi Energy regime. It suggests that the entire valence band electronic structure, not merely the Fermiology, may provide insight into the nature of high temperature superconducting cuprates.
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We discuss our measurements of the 2D-angular correlation of positron annihilation radiation (ACAR) in La(sub 2)CuO(sub 4), YBa(sub 2)Cu(sub 3)O(sub 7) (YBCO), and NiO. The measurements for NiO are the first such 2D-ACAR measurements; the... more
We discuss our measurements of the 2D-angular correlation of positron annihilation radiation (ACAR) in La(sub 2)CuO(sub 4), YBa(sub 2)Cu(sub 3)O(sub 7) (YBCO), and NiO. The measurements for NiO are the first such 2D-ACAR measurements; the YBCO results are of a higher statistical quality than previously reported in the literature. The data are compared with complementary theoretical calculations and with each other. We discuss the implication of our analysis for ACAR studies of similar and related systems.
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Materials Science Forum Vols. 105-110 251 x 0.143 milliradian cells, at an instrumental angular resolution of 0.72 mrad ( 0.76 - 0.80 mrad when the effect of positron motion is included) and with the specimens at... more
Materials Science Forum Vols. 105-110 251 x 0.143 milliradian cells, at an instrumental angular resolution of 0.72 mrad ( 0.76 - 0.80 mrad when the effect of positron motion is included) and with the specimens at 300KunderavacuumoflO-6torr. The developing spectra ...
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Room temperature infrared-and optical-spectroscopic measurements are reported on brominated YBa2Cu306. 2 single-crystal samples. Incorporation of bromine in thelattice was observed in both Auger electron and infrared-spectroscopy... more
Room temperature infrared-and optical-spectroscopic measurements are reported on brominated YBa2Cu306. 2 single-crystal samples. Incorporation of bromine in thelattice was observed in both Auger electron and infrared-spectroscopy experiments but the exact lattice site for bromine dopant atoms remains unknown. Five of the six in-plane infrared-active E phonon modes were observed in YBa2Cu306. 2Br „samples and phonon frequency softening was observed for the 591-cm phonon [Cu (2)-O (2) in-plane stretch] mode. The ...
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We report new measurements of the electron positron momentum spectra of YBa2Cu3O(7-x) performed with ultra-high statistical precision. These data differ from previous results in two significant respects: They show the D(sub 2) symmetry... more
We report new measurements of the electron positron momentum spectra of YBa2Cu3O(7-x) performed with ultra-high statistical precision. These data differ from previous results in two significant respects: They show the D(sub 2) symmetry appropriate for untwinned crystals and, more importantly, they show unmistakable, statistically significant, discontinuities that are evidence of a major Fermi surface section. These results provide a partial answer to a question of special significance to the study of high temperature superconductors i.e., the distribution of the electrons in the material, the electronic structure. Special consideration has been given both experimentally and theoretically to the existence and shape of a Fermi surface in the materials and to the superconducting gap. There are only three experimental techniques that can provide details of the electronic structure at useful resolutions. They are angular correlation of positron annihilation radiation, ACAR, angle resolved photo emission, PE, and de Haas van Alphen measurements.
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As a consequence of the unusual nature of plutonium's electronic structure, point- and extended-defects are expected to, and do exhibit extraordinary properties. Low temperature magnetic susceptibility measurements on Pu and... more
As a consequence of the unusual nature of plutonium's electronic structure, point- and extended-defects are expected to, and do exhibit extraordinary properties. Low temperature magnetic susceptibility measurements on Pu and fcc-Pu(Ga) show that the magnetic susceptibility increases as a function of time, yet upon annealing the specimen returns to its initial magnetic susceptibility. This excess magnetic susceptibility (EMS) arises from the α-decay and U recoil damage cascades which produce vacancy and interstitials as point and extended defects. The time dependence of the EMS leads to an estimate of the number of atoms influenced by each α-decay, as well as a temperature dependence well described by a Curie-Weiss law. These results will be described in context of recent time dependent studies of the elastic modulus in delta Pu. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
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ABSTRACTThe role of oxide nanoparticles in cavity formation of a nano-oxide-dispersed ferritic steel subjected to (Fe + He) dual-ion and (Fe + He + H) triple-ion irradiations has been studied using transmission electron microscopy to... more
ABSTRACTThe role of oxide nanoparticles in cavity formation of a nano-oxide-dispersed ferritic steel subjected to (Fe + He) dual-ion and (Fe + He + H) triple-ion irradiations has been studied using transmission electron microscopy to elucidate the synergistic effects of helium and hydrogen on radiation tolerance of nano-oxide-dispersed ferritic steel for fusion energy systems. The effect of oxide nanoparticles on suppressing radiation-induced void swelling is clearly revealed from the observation of preferred trapping of helium bubbles at oxide nanoparticles, which results in a unimodal distribution of cavities in the (Fe + He) dual-ion irradiated specimen. An adverse effect of hydrogen implantation, however, is revealed from the observation of a bimodal distribution of cavities with large and facetted voids in association with the formation of HFe5O8-based hydroxide in local regions of the (Fe + He + H) triple-ion irradiated specimen.
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ABSTRACT One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D ACAR) data have been obtained as a function of temperature between 293 and 903K for single crystals of aluminium. The 2D ACAR... more
ABSTRACT One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D ACAR) data have been obtained as a function of temperature between 293 and 903K for single crystals of aluminium. The 2D ACAR data are compared with calculated 2D ACAR spectra for positrons annihilating from the Bloch state and from monovacancy- and divacancy-trapped states. The theoretical formalism incorporates many-body enhancement effects into supercell band-structure calculations for the defects; lattice constants appropriate to the experimental temperatures were used. Assuming the consequences of dynamic temperature effects to be small, the experimental 2D ACAR results can be accounted for the fraction of monovacancy-trapped positrons increasing with temperature, along with an additional and continually increasing contribution from divacancy-trapped positrons at high temperatures (above 613K). The analysis indicates that about 44% of the trapped positrons annihilate from a divacancy-trapped state at 903K. Comparison of these results with those from previous measurements concerning the equilibrium vacancy ensemble in aluminium indicates that the ratio of positron trapping rates at divacancies and monovacancies ( mu 2v/ mu 1v) is about two. The present results regarding the contributions from divacancies are found to be consistent with those from the quantitative analysis of the peak-count rate 1D ACAR data using a monovacancy-divacancy analysis, which is presented elsewhere.
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The temperature dependence of the Doppler-broadening lineshape parameter has been studied for Cu in the temperature range 30-1040 degrees C, with special attention given to the prevacancy region (T<500 degrees C). Effects attributable... more
The temperature dependence of the Doppler-broadening lineshape parameter has been studied for Cu in the temperature range 30-1040 degrees C, with special attention given to the prevacancy region (T<500 degrees C). Effects attributable to positron trapping were observed in the prevacancy region for samples annealed at temperatures T500 degrees C allowed a quantitative comparison to be made between the prevacancy traps and thermally generated vacancies. This comparison permitted a determination of both the fraction of positrons trapped in the prevacancy region and the lineshape parameter characteristic of annihilation in the prevacancy traps. It was found that the fraction of positrons trapped in the prevacancy temperature region depends upon the thermal and mechanical history of the sample, and possibly also on its impurity content. In addition, two possible explanations of the prevacancy trapping are discussed.
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ABSTRACT The temperature dependences of the Doppler-broadening lineshape parameter W and the positron lifetime have been measured for positron annihilation taking place in Au in the prevacancy temperature range 27K to 592K. The results... more
ABSTRACT The temperature dependences of the Doppler-broadening lineshape parameter W and the positron lifetime have been measured for positron annihilation taking place in Au in the prevacancy temperature range 27K to 592K. The results are consistent with a linear temperature dependence of these annihilation parameters. It is suggested that this observation represents correctly the intrinsic behaviour of the positron in the Au lattice. The results are compared with earlier work over similar temperature ranges, which has shown additional contributions to these annihilation characteristics.
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Magnetic isochronal annealing curves were measured on specimens of self damaged α-Pu and several δ-Pu alloys stabilized by Ga and Am. These results are compared to one another and to isochronal resistivity annealing curves, where... more
Magnetic isochronal annealing curves were measured on specimens of self damaged α-Pu and several δ-Pu alloys stabilized by Ga and Am. These results are compared to one another and to isochronal resistivity annealing curves, where distinct differences are observed between the magnetic and resistive annealing for the case of δ-Pu. The first stage of annealing observed in the resistivity measurements is largely missing from the magnetic measurements, indicating that interstitials contribute little if any signal to the magnetization, while the onset of vacancy migration is strongly reflected in the magnetization signal.
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ABSTRACT A monovacancy-model analysis of new temperature-dependent (in the range 293-903K) data of the peak-count rate, long-slit angular correlation of annihilation radiation (1D ACAR) for Al single crystals yields an apparent value for... more
ABSTRACT A monovacancy-model analysis of new temperature-dependent (in the range 293-903K) data of the peak-count rate, long-slit angular correlation of annihilation radiation (1D ACAR) for Al single crystals yields an apparent value for the monovacancy formation enthalpy (H1vF) of (0.76+or-0.04) eV. However, lifetime experiments of lower temperatures (293-645K) have yielded H1vF=(0.66+or-0.02) eV. A constrained monovacancy-divacancy analysis of the 1D ACAR data, incorporating theoretical predictions of the relative peak-count rates arising from monovacancy- and divacancy-trapped positrons, can resolve this apparent discrepancy between the lifetime results and momentum measurements (Doppler broadening or angular correlation) of the vacancy formation enthalpy in Al. This analysis yields a divacancy binding enthalpy of H2vb=(0.30+or-0.13) eV, and indicates that at the melting point about 60% of the positrons annihilate from divacancy-trapped states in Al, consistent with the interpretation of recent 2D ACAR results. Introduction of the ratio of the positron trapping rate into divacancies to that into monovacancies, mu 2v/ mu 1v, as deduced from the jellium-model calculations of McMullen et al. (1981) allows one to estimate the divacancy binding entropy S2vb as well. The results are compared with those of previous investigations of vacancy formation and self-diffusion in Al.
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... Rev. 134, B1269 (1964) . S. Tanaka, M. Furukawa, S. Iwata, M. Yaki, H. Amano, and T. Mikumo, J. Phys. Soc. Japan 15, 2125 (1960) [CrossRef][CAS]. ... 92, 1 (1967) [ADS];[CAS]; ND Dudey and TT Sugihara, Phys. Rev. 139, B896 (1965) ; DG... more
... Rev. 134, B1269 (1964) . S. Tanaka, M. Furukawa, S. Iwata, M. Yaki, H. Amano, and T. Mikumo, J. Phys. Soc. Japan 15, 2125 (1960) [CrossRef][CAS]. ... 92, 1 (1967) [ADS];[CAS]; ND Dudey and TT Sugihara, Phys. Rev. 139, B896 (1965) ; DG Sarantites and BD Pate, Nucl. Phys. ...
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One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D-ACAR) data have been obtained between 293 and 903 K for single crystals of aluminum. The peak counting rates vs temperature, which were... more
One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D-ACAR) data have been obtained between 293 and 903 K for single crystals of aluminum. The peak counting rates vs temperature, which were measured using the 1D-ACAR technique, provide a model independent value for the temperature dependence of the positron trapping probability. Using these results it is possible to strip out the Bloch state contribution from the observed 2D-ACAR surfaces and then compare the resulting defect ACAR surfaces to calculated 2D-ACAR surfaces for positrons annihilating from the Bloch, monovacancy, and divacancy-trapped states. The result of this comparison is that the presence of an increasing equilibrium divacancy population is consistent with the observed temperature dependence of ACAR data at high temperature in Al and that the present results when compared to earlier studies on Al indicate that the ratio of the trapping rates at divacancies and monovacanci...
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As a consequence of the unusual nature of plutonium's electronic structure, point-and extended-defects are expected to, and do exhibit extraordinary properties. Low temperature magnetic susceptibility measurements on Pu and fcc-Pu... more
As a consequence of the unusual nature of plutonium's electronic structure, point-and extended-defects are expected to, and do exhibit extraordinary properties. Low temperature magnetic susceptibility measurements on Pu and fcc-Pu (Ga) show that the magnetic ...
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In the Pu 1-x Am x system, stable fee phases are obtained for 0.05<x<0.75, and the lattice parameters increase with the Am content. Both elements decay by α-emission creating cascades of vacancies, interstitials, and their... more
In the Pu 1-x Am x system, stable fee phases are obtained for 0.05<x<0.75, and the lattice parameters increase with the Am content. Both elements decay by α-emission creating cascades of vacancies, interstitials, and their aggregates. As damage accumulates, it is accompanied by an increase in the magnetic susceptibility. Preliminary results of radiation damage studies on the magnetic properties of Pu(Am) alloys are reported here.
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Recently published experimental positron annihilation data in metals have demonstrated exceptional temperature-dependent behavior in the prevacancy region. However, the magnitude of these effects seems at present to scatter widely among... more
Recently published experimental positron annihilation data in metals have demonstrated exceptional temperature-dependent behavior in the prevacancy region. However, the magnitude of these effects seems at present to scatter widely among different observers. New lifetime and Doppler-broadening results for Au between 30 and 590°K are presented and compared to results obtained in other laboratories. Doppler-broadening results obtained for Cu in the temperature region 300 to 1310°K demonstrate that some temperature-dependent structure observed in the prevacancy region is related to the thermal history of the sample.
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... Luke L. Hsiung1, Michael J. Fluss1, Joshua D. Kuntz1, Bassem S. El-Dasher1, B. William Choi1, Scott J. Tumey1, Akihiko Kimura2 ... 307-311 (2002) 749. 3. EE Bloom, JT Busby, CE Duty, PJ Maziasz, TE McGreevy, BE Nelson, BA Pint, PF... more
... Luke L. Hsiung1, Michael J. Fluss1, Joshua D. Kuntz1, Bassem S. El-Dasher1, B. William Choi1, Scott J. Tumey1, Akihiko Kimura2 ... 307-311 (2002) 749. 3. EE Bloom, JT Busby, CE Duty, PJ Maziasz, TE McGreevy, BE Nelson, BA Pint, PF Tortorelli, SJ Zinkle, J. Nucl. Mater. ...
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We review results from previous muon spin relaxation (µSR) measurements in applied fields of H0 = 0 and 0.25 T which established an upper limit for the ordered or disordered frozen spin moment above T = 4 K in δ-Pu (4.3 at. % Ga) of µ ord... more
We review results from previous muon spin relaxation (µSR) measurements in applied fields of H0 = 0 and 0.25 T which established an upper limit for the ordered or disordered frozen spin moment above T = 4 K in δ-Pu (4.3 at. % Ga) of µ ord ≤ 10 −3 µB. In addition, we present new data in H0 = 0.25 T and 2 T applied field on a highly annealed δ-Pu (4.3 at. % Ga) sample. Neither the muon Knight shift (H0 = 2 T) nor the inhomogeneous linewidths in the new sample show appreciable temperature dependence below about T = 60 K, also consistent with no spin freezing. Recent theoretical arguments advanced to explain these results are mentioned.
K. Ohishi, R.H. Heffner, 2 G.D. Morris, 3 E.D. Bauer, M.J. Graf, J.-X. Zhu, L.A. Morales, J.L. Sarrao, M.J. Fluss, D.E. MacLaughlin, L. Shu, W. Higemoto, and T.U. Ito 6 Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan Los Alamos... more
K. Ohishi, R.H. Heffner, 2 G.D. Morris, 3 E.D. Bauer, M.J. Graf, J.-X. Zhu, L.A. Morales, J.L. Sarrao, M.J. Fluss, D.E. MacLaughlin, L. Shu, W. Higemoto, and T.U. Ito 6 Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan Los Alamos National Laboratory, Los Alamos, New Mexico 87545 USA TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C., Canada V6T 2A3 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 USA Department of Physics, University of California, Riverside, California 92521 USA Department of Physics, Tokyo Institute of Technology, Megro-ku, Tokyo 152-8551, Japan (Dated: May 31, 2018)
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Research Interests: Physics, Condensed Matter Physics, RADIATION DAMAGE, Crystal structure, Magnetic Susceptibility, and 11 morePhase transition, Spin Relaxation, Temperature Dependence, Room Temperature, Quantum Criticality, Low Temperature, Thermal annealing, Physical Properties, PLUTONIUM, Component Model, and phase diagram
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Plutonium possesses the most complicated phase diagram in the periodic table, driven by the complexities of overlapping 5 f electron orbitals. Despite the importance of the 5 f electrons in defining the structure and physical properties,... more
Plutonium possesses the most complicated phase diagram in the periodic table, driven by the complexities of overlapping 5 f electron orbitals. Despite the importance of the 5 f electrons in defining the structure and physical properties, there is no experimental evidence that these electrons localize to form magnetic moments in pure Pu. Instead, a large temperature-independent Pauli susceptibility indicates that they form narrow conduction bands. Radiation damage from the α-particle decay of Pu creates numerous defects in the crystal structure, which produce a significant temperature-dependent magnetic susceptibility, χ( T ), in both α-Pu and δ-Pu (stabilized by 4.3 atomic percent Ga). This effect can be removed by thermal annealing above room temperature. By contrast, below 35 K the radiation damage is frozen in place, permitting the evolution in χ( T ) with increasing damage to be studied systematically. This result leads to a two-component model consisting of a Curie–Weiss term a...