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Shu, L.

Publications and source records attributed to Shu, L..

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Electronic structure study of LaCoIn 5 and its comparison with CeCoIn 5

A central key to understanding heavy-fermion systems involves revealing how itinerant low-energy excitations emerge from local f moments. An effective way to understand the f -electron behavior is to compare the electronic structure of f -electron compounds with a reference isostructural compound with no f electrons. Here we present a systematic electronic structure study of LaCoIn 5 , which is a non- f reference compound of the heavy-fermion superconductor CeCoIn 5 . Our angle-resolved photoemission spectroscopy study of the three-dimensional Fermi surface and band structure of LaCoIn 5 highlights the rather three-dimensional electronic character of this compound. The conduction bands of LaCoIn 5 are almost identical to that of CeCoIn 5 , though obvious differences can be found in the low-energy electronic structure. Finally, we give a quantitative analysis of the Fermi pocket change in LaCoIn 5 and CeCoIn 5 , which may be helpful for understanding the important “large” and “small” Fermi surface issue in heavy-fermion compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ar + H{sub 2} Plasma Interacting with Lithium-Filled Capillary Porous Structure

Ar + H{sub 2} plasma interacting with liquid lithium was carried out on a one-cathode linear plasma device (SCU-PSI). The lithium sample was covered with capillary porous structure (CPS). It is found that the electron temperature of applied plasma ranged from ~0–1 eV and electron density ranged from 0.1 × 10{sup 20} to 1 × 10{sup 20} m{sup −3}. The experimental results indicate that a reduction in the electron temperature and the lithium evaporation is found as the percentage of H{sub 2} increases When the ratio of argon and hydrogen keeps constant, the electron temperature and lithium evaporation increase with applied input power, respectively. The retention of hydrogen atoms in lithium surface results in reducing the lithium evaporation. The XRD analysis result shows that during plasma radiation no LiH is formed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Band Dependent Interlayer f -Electron Hybridization in CeRhIn 5

A key issue in heavy fermion research is how subtle changes in the hybridization between the 4 f (5 f ) and conduction electrons can result in fundamentally different ground states. CeRhIn 5 stands out as a particularly notable example: when replacing Rh with either Co or Ir, antiferromagnetism gives way to superconductivity. In this photoemission study of CeRhIn 5 , we demonstrate that the use of resonant angle-resolved photoemission spectroscopy with polarized light allows us to extract detailed information on the 4 f crystal field states and details on the 4 f and conduction electron hybridization, which together determine the ground state. We directly observe weakly dispersive Kondo resonances of f electrons and identify two of the three Ce4 f $^{1}_{5/2}$ crystal-electric-field levels and band-dependent hybridization, which signals that the hybridization occurs primarily between the Ce 4 f states in the CeIn 3 layer and two more three-dimensional bands composed of the Rh 4 d and In 5 p orbitals in the RhIn 2 layer. Our conclusions allow us to connect the properties observed at elevated temperatures with the unusual low-temperature properties of this enigmatic heavy fermion compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce 1−x Yb x CoIn 5

The neutron spin resonance is a collective magnetic excitation that appears in the unconventional copper oxide, iron pnictide and heavy fermion superconductors. Although the resonance is commonly associated with a spin-exciton due to the d(s ± )-wave symmetry of the superconducting order parameter, it has also been proposed to be a magnon-like excitation appearing in the superconducting state. Here we use inelastic neutron scattering to demonstrate that the resonance in the heavy fermion superconductor Ce 1−x Yb x CoIn 5 with x=0, 0.05 and 0.3 has a ring-like upward dispersion that is robust against Yb-doping. By comparing our experimental data with a random phase approximation calculation using the electronic structure and the momentum dependence of the d x 2 -y 2 -wave superconducting gap determined from scanning tunnelling microscopy (STM) for CeCoIn 5 , we conclude that the robust upward-dispersing resonance mode in Ce 1−x Yb x CoIn 5 is inconsistent with the downward dispersion predicted within the spin-exciton scenario.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Universal heat conduction in Ce 1-x Yb x CoIn 5 : Evidence for robust nodal d-wave superconducting gap

In the heavy-fermion superconductor Ce 1-x Yb x CoIn 5 , Yb doping was reported to cause a possible change from nodal d-wave superconductivity to a fully gapped d-wave molecular superfluid of composite pairs near x ≈ 0.07 (nominal value x nom = 0.2). Here we present systematic thermal conductivity measurements on Ce 1-x Yb x CoIn 5 (x = 0.013, 0.084, and 0.163) single crystals. The observed finite residual linear term κ 0 /T is insensitive to Yb doping, verifying the universal heat conduction of the nodal d-wave superconducting gap in Ce 1-x Yb x CoIn 5 . Similar universal heat conduction is also observed in the CeCo(In 1–y Cd y ) 5 system. Furthermore, these results reveal a robust nodal d-wave gap in CeCoIn 5 upon Yb or Cd doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Resolution of the discrepancy between the variation of the physical properties of Ce 1- x Yb x CoIn 5 single crystals and thin films with Yb composition

The extraordinary electronic phenomena including an Yb valence transition, a change in Fermi surface topology, and suppression of the heavy fermion quantum critical field at a nominal concentration x≈0.2 have been found in the Ce 1- x Yb x CoIn 5 system. These phenomena have no discernable effect on the unconventional superconductivity and normal-state non-Fermi liquid behaviour that occur over a broad range of x up to ~0.8. However, the variation of the coherence temperature T* and the superconducting critical temperature T c with nominal Yb concentration x for bulk single crystals is much weaker than that of thin films. To determine whether differences in the actual Yb concentration of bulk single crystals and thin film samples might be responsible for these discrepancies, we employed Vegard’s law and the spectroscopically determined values of the valences of Ce and Yb as a function of x to determine the actual composition x act of bulk single crystals. This analysis is supported by energy-dispersive X-ray spectroscopy, wavelength-dispersive X-ray spectroscopy, and transmission X-ray absorption edge spectroscopy measurements. The actual composition x act is found to be about one-third of the nominal concentration x up to x~0.5, and resolves the discrepancy between the variation of the physical properties of Ce 1- x Yb x CoIn 5 single crystals and thin films with Yb concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Simulation of the full-core pin-model by JMCT Monte Carlo neutron-photon transport code

Since the large numbers of cells over a million, the tallies over a hundred million and the particle histories over ten billion, the simulation of the full-core pin-by-pin model has become a real challenge for the computers and the computational methods. On the other hand, the basic memory of the model has exceeded the limit of a single CPU, so the spatial domain and data decomposition must be considered. JMCT (J Monte Carlo Transport code) has successful fulfilled the simulation of the full-core pin-by-pin model by the domain decomposition and the nested parallel computation. The k{sub eff} and flux of each cell are obtained. (authors)

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Insensitivity of the pressure dependences of characteristic energy scales in Ce 1–x R x CoIn₅ (R=Yb,Y,Gd) to the electronic configuration of the rare-earth ion

Cooperative Ce and Yb valence fluctuations have recently been proposed as the mechanism responsible for stabilizing correlated electron phenomena in Ce₁₋ x YbxCoIn₅ over an unexpectedly large range of concentrations. In order to better understand the origins and character of this stability, we have measured the effect of applied pressure on relevant energy scales such as the superconducting critical (T c ) and Kondo-lattice coherence (T*) temperatures of Ce₁₋ x R x CoIn₅ with R=Yb, Y, and Gd. Electrical resistivity measurements were performed under applied pressure on samples doped with intermediate-valent Yb and stable-valent Gd and Y, and the responses of Tc and T* to increased pressure in these systems are compared. The character of T c (P) and T*(P) in Ce₁₋ x R x CoIn₅ depends only on their respective ambient-pressure values T c (0) and T*(0), independent of the electronic configuration of R or concentration x. The consequences of this result are discussed within the context of possible cooperative valence fluctuations in Ce₁₋ x Yb x CoIn₅.

White, B. D.↗
NASA NTRS1985

A cascaded coding scheme for error control

A cascade coding scheme for error control is investigated. The scheme employs a combination of hard and soft decisions in decoding. Error performance is analyzed. If the inner and outer codes are chosen properly, extremely high reliability can be attained even for a high channel bit-error-rate. Some example schemes are evaluated. They seem to be quite suitable for satellite down-link error control.

Shu, L.↗