Showing papers by "Argonne National Laboratory published in 1995"
TL;DR: The authors present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which they designate Argonne {upsilon}{sub 18}.
Abstract: The authors present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which they designate Argonne {upsilon}{sub 18}. The model has a charge-independent part with fourteen operator components that is an updated version of the Argonne {upsilon}{sub 14} potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen pp and np scattering data base, low-energy nn scattering parameters, and deuteron binding energy. With 40 adjustable parameters it gives a {chi}{sup 2} per datum of 1.09 for 4,301 pp and np data in the range 0--350 MeV.
2,409 citations
TL;DR: In this paper, a rigorous analysis of the annihilation decay rates of heavy quarkonium states is presented, with coefficients that can be computed using perturbation theory in non-relativistic QCD.
Abstract: A rigorous QCD analysis of the inclusive annihilation decay rates of heavy quarkonium states is presented. The effective-field-theory framework of nonrelativistic QCD is used to separate the short-distance scale of annihilation, which is set by the heavy quark mass M, from the longer-distance scales associated with quarkonium structure. The annihilation decay rates are expressed in terms of nonperturbative matrix elements of four-fermion operators in nonrelativistic QCD, with coefficients that can be computed using perturbation theory in the coupling constant ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$(M). The matrix elements are organized into a hierarchy according to their scaling with v, the typical velocity of the heavy quark. An analogous factorization formalism is developed for the production cross sections of heavy quarkonium in processes involving momentum transfers of order M or larger. The factorization formulas are applied to the annihilation decay rates and production cross sections of S-wave states at next-to-leading order in ${\mathit{v}}^{2}$ and P-wave states at leading order in ${\mathit{v}}^{2}$.
1,882 citations
TL;DR: In this paper, the existence of the top quark was established using a data sample of collisions at the Fermilab National Ensemble (CDF) collected with the Collider Detector.
Abstract: We establish the existence of the top quark using a $67{\mathrm{pb}}^{\ensuremath{-}1}$ data sample of $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ collected with the Collider Detector at Fermilab (CDF). Employing techniques similar to those we previously published, we observe a signal consistent with $t\overline{t}$ decay to $\mathrm{WWb}\overline{b}$, but inconsistent with the background prediction by $4.8\ensuremath{\sigma}$. Additional evidence for the top quark is provided by a peak in the reconstructed mass distribution. We measure the top quark mass to be $176\ifmmode\pm\else\textpm\fi{}8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}10(\mathrm{syst})\mathrm{GeV}{/c}^{2}$, and the $t\overline{t}$ production cross section to be ${6.8}_{\ensuremath{-}2.4}^{+3.6}\mathrm{pb}$.
1,022 citations
TL;DR: The development and deployment of novel separations technologies, such as electrodialysis with bipolar membranes, extractive distillations integrated with fermentation, and chemical conversion, can enable low-cost production with continuous processes in large-scale operations and can use environmentally sound processes to produce environmentally useful products from lactic acid.
Abstract: Lactic acid has been an intermediate-volume specialty chemical (world production ∼ 40,000 tons/yr) used in a wide range of food processing and industrial applications. Lactic acid has the potential of becoming a very large volume, commodity-chemical intermediate produced from renewable carbohydrates for use as feedstocks for biodegradable polymers, oxygenated chemicals, plant growth regulators, environmentally friendly ‘green’ solvents, and specialty chemical intermediates. The recent announcements of new development-scale plants for producing lactic acid and polymer intermediates by major U.S. companies, such as Cargill, Ecochem (DuPont/ConAgra), and Archer Daniels Midland, attest to this potential. In the past, efficient and economical technologies for the recovery and purification of lactic acid from crude fermentation broths and the conversion of lactic acid to the chemical or polymer intermediates had been the key technology impediments and main process cost centers. The development and deployment of novel separations technologies, such as electrodialysis (ED) with bipolar membranes, extractive distillations integrated with fermentation, and chemical conversion, can enable low-cost production with continuous processes in large-scale operations. The use of bipolar ED can virtually eliminate the salt or gypsum waste produced in the current lactic acid processes. Thus, the emerging technologies can use environmentally sound processes to produce environmentally useful products from lactic acid. The process economics of some of these processes and products can also be quite attractive. In this paper, the recent technical advances in lactic and polyactic acid processes are discussed. The economic potential and manufacturing cost estimates of several products and process options are presented. The technical accomplishments at Argonne National Laboratory (ANL) and the future directions of this program at ANL are discussed.
626 citations
25 Apr 1995
TL;DR: A scheduler was built that actually “worked” the way the users wanted it to work, and was unique in that user input and interaction were encouraged throughout the development process.
Abstract: During the past five years scientists discovered that modern UNIX workstations connected with ethernet and fiber networks could provide enough computational performance to compete with the supercomputers of the day. As this concept became increasingly popular, the need for distributed queuing and scheduling systems became apparent. Systems such as DQS from Florida State were developed and worked very well. Today, supercomputers, such as Argonne National Laboratory's IBM SP system, can provide more CPU and networking speed than can be obtained from these networks of workstations. These modern supercomputers look like clusters of workstations, however, so developers felt that the scheduling systems that were previously used on clusters of workstations should still apply. After trying to apply some of these scheduling systems to Argonne's SP environment, it became obvious that these two computer environments have very different scheduling needs. Recognizing this need and realizing that no one has addressed it, I developed a new scheduling system. The approach taken in creating this system was unique in that user input and interaction were encouraged throughout the development process. Thus, a scheduler was built that actually “worked” the way the users wanted it to work.
537 citations
TL;DR: It is confirmed that YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} satisfies the same universal relations in these quantities as the other high-{ital T}{sub {ital c}} superconducting cuprates.
Abstract: A direct determination of the relationship between ${\mathit{T}}_{\mathit{c}}$ and hole concentration p for ${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ is obtained by investigating the properties of the fully oxygen-deficient (\ensuremath{\delta}\ensuremath{\approxeq}1.0) compound for which p=x/2. Measurements of ${\mathit{T}}_{\mathit{c}}$, the thermoelectric power S, and bond-valence sums calculated from neutron-diffraction refinements for various values of x and \ensuremath{\delta} allow the full determination of the relations p=p(\ensuremath{\delta}), ${\mathit{T}}_{\mathit{c}}$=${\mathit{T}}_{\mathit{c}}$(p), and S=S(T,p) confirming that ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ satisfies the same universal relations in these quantities as the other high-${\mathit{T}}_{\mathit{c}}$ superconducting cuprates.
502 citations
TL;DR: In this article, the lattice of magnetic flux lines that can permeate a type ii superconductor, such as the high-transition-temperature copper oxide materials, was found to be first-order.
Abstract: The lattice of magnetic flux lines that can permeate a type ii superconductor, such as the high-transition-temperature copper oxide materials, melts from a solid-like stale to a liquid-like state at a temperature below the superconducting transition temperature. Contrary to the predictions of mean-field theory, this phase transition in Bi2Sr2CaCu2O8 is found to be first-order. The vortex liquid discontinuously expands on freezing.
483 citations
TL;DR: In this paper, the structural properties of insertion electrodes with layered and spinel structures are discussed, and the use of (spinel) instead of lithiated carbon as anode is briefly discussed.
Abstract: Rechargeable lithium batteries that can be assembled in the discharged state with lithiated metal oxide cathodes and carbon anodes are being developed to minimize the safety hazards associated with batteries that use pure metallic lithium anodes. This paper reviews crystallographic aspects of insertion electrodes with layered and spinel structures . The use of (spinel) instead of lithiated carbon as the anode is briefly discussed. Emphasis is placed on the structural properties of insertion electrodes that control their stability during electrochemical cycling.
467 citations
TL;DR: In this paper, a quaternary amine-based liquid anion exchanger was used for the extraction of actinides from nitric and hydrochloric acids, which exhibited preferential retention of tetravalent actinide over a wide range of acidities.
437 citations
TL;DR: The validity of the results through a comparison of the analysis of an fcc lattice under hydrostatic tension with direct molecular-dynamics simulation is demonstrated, showing that crystal stability under stress (ideal strength) is not a question only of material property, and that even qualitative predictions require the inclusion of the effects of applied stress.
Abstract: Elastic stability criteria are derived for homogeneous lattices under arbitrary but uniform external load. These conditions depend explicitly on the applied stress and reduce, in the limit of vanishing load, to the criteria due to Born, involving only the elastic constants of the crystal. By demonstrating the validity of our results through a comparison of the analysis of an fcc lattice under hydrostatic tension with direct molecular-dynamics simulation, we show that crystal stability under stress (ideal strength) is not a question only of material property, and that even qualitative predictions require the inclusion of the effects of applied stress. General implications of our findings, as well as relevance to stability phenomena in melting, polymorphism, crack nucleation, and solid-state amorphization, are discussed.
432 citations
TL;DR: The energies of {Sup 3}H, {sup 3}He, and {sup 4}He ground states, the {sup 2{minus}}/2 and {Sup 1{minus}/2 scattering states, and the 3{sup +} and 0{Sup +} excited states of {sup 6}Li have been accurately calculated with the Green`s function Monte Carlo method using realistic models of two- and three-nucleon interactions.
Abstract: The energies of ${}^{3}\mathrm{H}$, ${}^{3}\mathrm{He}$, and ${}^{4}\mathrm{He}$ ground states, the ${\frac{3}{2}}^{{}^{\ensuremath{-}}}$ and ${\frac{1}{2}}^{{}^{\ensuremath{-}}}$ scattering states of ${}^{5}\mathrm{He}$, the ground states of ${}^{6}\mathrm{He}$, ${}^{6}\mathrm{Li}$, and ${}^{6}\mathrm{Be}$, and the ${3}^{+}$ and ${0}^{+}$ excited states of ${}^{6}\mathrm{Li}$ have been accurately calculated with the Green's function Monte Carlo method using realistic models of two- and three-nucleon interactions. The splitting of the $A\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3$ isospin $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\frac{1}{2}$ and $A\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}6$ isospin $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$, ${J}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0}^{+}$ multiplets is also studied. The observed energies and radii are generally well reproduced, however, some definite differences between theory and experiment can be identified.
TL;DR: In this paper, the fundamental theorems of quantum chromodynamics are discussed and a discussion of the global fitting approach to the determination of parton distributions in nucleons is presented.
Abstract: The elements, theoretical basis, and experimental status of perturbative quantum chromodynamics are presented. Relevant field-theoretic methods are introduced at a nonspecialist level, along with a review of the basic ideas and methods of the parton model. This is followed by an account of the fundamental theorems of quantum chromodynamics, which generalize the parton model. Summaries of the theoretical and experimental status of the most important hard-scattering processes are then given, including electron-positron annihilation, deeply inelastic scattering, and hard hadron-hadron scattering, as induced both by electoweak interactions and by quantum chromodynamics directly. In addition, a discussion is presented of the global fitting approach to the determination of parton distributions in nucleons.
TL;DR: The phonon density of states was measured by observing the nuclear resonant fluorescence of {sup 57}Fe versus the energy of incident x rays from a synchrotron radiation beam.
Abstract: The phonon density of states was measured by observing the nuclear resonant fluorescence of ${}^{57}$Fe versus the energy of incident x rays from a synchrotron radiation beam. An energy resolution of 6 meV was achieved by use of high-resolution crystal optics for the incident beam. Extremely low background levels were obtained via time discrimination of the nuclear fluorescent radiation.
TL;DR: It is suggested that growth is coordinated between VAM hyphae and root morphology, which in turn are constrained by plant community composition and soil nutrient and moisture conditions.
Abstract: External hyphae of vesicular-arbuscular mycorrhizal (VAM) fungi were quantified over a growing season in a reconstructed tallgrass prairie and an ungrazed cool-season pasture. In both sites, hyphal lengths increased throughout the growing season. Peak external hyphal lengths were 111 m cm−3 of soil in the prairie and 81 m cm−3 of soil in the pasture. These hyphal lengths calculate to external hyphal dry weights of 457 μg cm−3 and 339 μg cm−3 of soil for prairie and pasture communities, respectively. The relationships among external hyphal length, root characteristics, soil P and soil moisture were also determined. Measures of gross root morphology [e.g., specific root length (SRL) and root mass] have a strong association with external hyphal length. Over the course of the study, both grassland communities experienced a major drought event in late spring. During this period a reduction in SRL occurred in both the pasture and prairie without a measured reduction in external hyphal length. Recovery for both the pasture and prairie occurred not by increasing SRL, but rather by increasing external hyphal length. This study suggests that growth is coordinated between VAM hyphae and root morphology, which in turn, are constrained by plant community composition and soil nutrient and moisture conditions.
TL;DR: In this paper, perovskite type oxides (ABO3) containing transition metals on the B-site show mixed (electronic/ionic) conductivity, and extruded tubes of these materials have been evaluated in a reactor operating at ca. 850°C for direct conversion of methane into syngas (CO + H2) in the presence of a reforming catalyst.
Abstract: Several perovskite-type oxides (ABO3) containing transition metals on the B-site show mixed (electronic/ionic) conductivity. These mixed-conductivity oxides are promising materials for oxygen-permeating membranes that can operate without electrodes or external electrical circuitry. Oxides in the system LaSrFeCoO permeate large amounts of oxygen, and extruded tubes of these materials have been evaluated in a reactor operating at ca. 850°C for direct conversion of methane into syngas (CO + H2) in the presence of a reforming catalyst. Methane conversion efficiencies of > 99% were observed, and some of the reactor tubes have been operated for over 1000 h. Membrane tubes were fabricated from calcined powders by a plastic extrusion technique. Ceramic powders in the LaSrFeCoO system were made by solid-state reaction of the constituent carbonates, oxides, and/or nitrates. The chemical-phase behavior of the ceramic powders with varying stoichiometries were studied by high-temperature in-situ X-ray diffraction (XRD) as a function of oxygen partial pressure. The sintered extruded tubes were also characterized by XRD and scanning electron microscopy.
TL;DR: The three-dimensional structure of choleragen, along with those of related toxins from Shigella dysenteria and Bordetella pertussis, offer a first step towards the rational design of new vaccines and anti-microbial agents.
TL;DR: In this paper, a brief overview of the present understanding of the mechanical properties of nanophase metals is presented, including grain boundary sliding and other microstructural features, as well as grain size changes are discussed.
TL;DR: In this paper, the authors examined the starting material and fractured membranes using a combination of X-ray diffraction and thermogravimetric analyses and found that the first type of fracture was the consequence of an oxygen gradient in the membrane, pointing from the reaction side to the air side, leading to fracture.
Abstract: In the course of generating synthesis gas (H2, CO) from methane, we have observed two types of fractures occurring on the Sr(Co, Fe)Ox-type oxygen membrane reactors The first type occurred shortly after the reaction started and the second type often occurred days after the reaction To determine the causes of these fractures, we have examined the starting material and fractured membranes using a combination of X-ray diffraction and thermogravimetric analyses We found that the first type of fracture was the consequence of an oxygen gradient in the membrane, pointing from the reaction side to the air side This causes a lattice mismatch inside the membrane, leading to fracture The second type of fracture, however, was the result of a chemical decomposition We found that the Sr(Co, Fe)Ox-type membrane had been reduced to SrCO3, and elemental Co and Fe by the synthesis gas generated in the reaction The decomposition causes enormous expansion leading to a large crack along the axis of tube
TL;DR: In this article, a photorefractive gain ratio of 1.88 was achieved with low applied electric fields (0.4 kilovolts per centimeter) requiring only a 1.5volt battery and low light intensities (100 milliwatts per square centimeter).
Abstract: Liquid crystalline composite materials have been prepared that are strongly photorefractive. Nematic liquid crystals were doped with both electron donor and electron acceptor molecules that undergo facile, photoinduced, electron transfer reactions to yield mobile ions. A photorefractive gain ratio of 1.88 was observed. This gain ratio was achieved with low applied electric fields (0.4 kilovolts per centimeter) requiring only a 1.5-volt battery and low light intensities (100 milliwatts per square centimeter) in samples 37 to 88 micrometers thick that showed no loss in gain over a 6-month period.
TL;DR: In this paper, the radial and azimuthal position of actin-tropomyosin gels was adjusted to fit the X-ray fiber diffraction patterns from oriented actin tropomyosins gels at a resolution of 1/8 A-1.
TL;DR: In this article, a numerical simulation of forced convective incompressible flow through porous beds was performed in terms of non-dimensional parameters that successfully cast together all the pertinent influencing effects.
Abstract: The present work centers around the numerical simulation of forced convective incompressible flow through porous beds. Inertial as well as viscous effects are considered in the momentum equation. The mathematical model for energy transport was based on the two-phase equation model, which does not employ local thermal equilibrium assumption between the fluid and the solid phases. The transport processes for two different types of boundary conditions are studied. The analysis was performed in terms of nondimensional parameters that successfully cast together all the pertinent influencing effects. Comparisons were made between our numerical findings and experimental results. Overall, the comparisons that were made for the constant wall heat flux boundary condition display good agreement.
TL;DR: Tight-binding fits to the normal-state dispersion and superlattice modulation effects are described and the anisotropic s-wave gap cos is found, which within a one-band BCS framework suggests the importance of next-near-neighbor Cu-Cu interactions.
Abstract: Recently, high-resolution angle-resolved photoemission spectroscopy has been used to determine the detailed momentum dependence of the superconducting gap in the high-temperature superconductor ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$. In this paper, we first describe tight-binding fits to the normal-state dispersion and superlattice modulation effects. We then discuss various theoretical models in light of the gap measurements. We find that the simplest model which fits the data is the anisotropic s-wave gap cos(${\mathit{k}}_{\mathit{x}}$)cos(${\mathit{k}}_{\mathit{y}}$), which within a one-band BCS framework suggests the importance of next-near-neighbor Cu-Cu interactions. Various alternative interpretations of the observed gap are also discussed, along with the implications for microscopic theories of high-temperature superconductors.
TL;DR: In this article, the results of static strain aging, stress relaxation, and strain rate change tests on 310s stainless steel foils, with and without hydrogen, have been presented to complement the stress-strain curves.
Abstract: Microscopic observations and the results of static strain aging, stress relaxation, and strain rate change tests on 310s stainless steel foils, with and without hydrogen, have been presented to complement the stress-strain curves in a previous article. The hydrogen-free specimens showed minute yield points during static strain aging, while the hydrogen-containing specimens demonstrated “preyield microstrain. ” Thermal activation analysis of the strain rate change and stress relaxation plots led to the conclusion that the activation area for dislocation motion is decreased by hydrogen. Microstructural examination with the scanning electron microscope (SEM) revealed extensive strain localization, while transmission electron microscopy (TEM) studies showed microtwinning and austenite faulting in hydrogenated specimens tested at room temperature. The relation of hydrogen-induced changes in plastic deformation to hydrogen embrittlement is discussed.
TL;DR: FORTRAN M is a small set of extensions to FORTRAN 77 that supports a modular approach to the design of message-passing programs that can be compiled efficiently for uniprocessors, shared-memory computers, distributed- memory computers, and networks of workstations.
TL;DR: In this paper, controlled field measurements of methane emissions at sites in Illinois and California (USA) using a closed chamber technique were conducted. But the results of these experiments were limited.
TL;DR: It is argued that {ital S}({omega}) represents critical scattering associated with a {ital T}=0 phase transition, whose origin lies with the magnetic screening of individual uranium ions.
Abstract: We have determined the magnetic response {ital S}({omega}) of UCu{sub 5{minus}{ital x}}Pd{sub {ital x}}({ital x}=1,1.5) for temperatures {ital T} ranging from 12 to 300 K and energy transfers {omega} from 0.5 to 200 meV. {ital S}({omega}) is virtually identical in the two compounds, displaying localized moment dynamics for {omega}{approx_gt}25 meV. For {omega}{lt}25 meV, temperature provides the only energy scale for the magnetic excitations with the dynamical susceptibility described by a universal scaling function {chi}{double_prime}({omega},{ital T}){similar_to}{omega}{sup {minus}1/3}{ital Z}({omega}/{ital T}). We argue that {ital S}({omega}) represents critical scattering associated with a {ital T}=0 phase transition, whose origin lies with the magnetic screening of individual uranium ions.
University of Illinois at Chicago1, University of Maryland, College Park2, Lawrence Livermore National Laboratory3, Massachusetts Institute of Technology4, Fermilab5, University of Pennsylvania6, University of Washington7, University of Wuppertal8, Max Planck Society9, Ohio University10, Harvard University11, University of Freiburg12, Argonne National Laboratory13, Hungarian Academy of Sciences14, University of California, San Diego15, Northwestern University16
TL;DR: The first precise measurements of F 2 in the low x and Q 2 range of the data were taken at Fermilab experiment 665 during 1991-1992 using liquid hydrogen and deuterium targets as discussed by the authors.
Abstract: The proton and deuteron structure functions F{sub 2}{sup p} and F{sub 2}{sup d} measured in inelastic muon scattering with an average beam energy of 470 GeV. The data were taken at Fermilab experiment 665 during 1991-1992 using liquid hydrogen and deuterium targets. The F{sub 2} measurements are reported in the range 0.0008 < x < 0.6 and 0.2 < Q{sup 2} < 75 GeV{sup 2}. These are the first precise measurements of F{sub 2} in the low x and Q{sub 2} range of the data. The E665 data overlap in x with the HERA data, and there is a smooth connection in Q{sup 2} between the two data sets. At high Q{sup 2} the E665 measurements are consistent with QCD-evolved leading twist structure function models. The data are qualitatively described by structure function models incorporating the hadronic nature of the photon at low Q{sup 2}. The Q{sup 2} and the W dependence of the data measure the transition in the nature of the photon between a point-probe at high Q{sup 2} and a hadronic object at low Q{sup 2}.
TL;DR: In this paper, PbTiO3 films were prepared by metalorganic chemical-vapor deposition on MgO(001) and LaAlO3 (001) oriented substrates, and the defect structure of the films, including grain tilting, threading dislocation density and 90° domain formation, was strongly dependent on the choice of substrate material.
Abstract: Epitaxial PbTiO3 films were prepared by metalorganic chemical‐vapor deposition on MgO(001)‐, SrTiO3(001)‐, and LaAlO3(001)‐oriented substrates. Four‐circle x‐ray diffraction, transmission electron microscopy, Rutherford backscattering (RBS) channeling, and optical waveguiding were performed to characterize the deposited films. Epitaxial, single‐crystal films were obtained on all three substrate materials under the same growth conditions. However, the defect structure of the films, including grain tilting, threading dislocation density, and 90° domain formation, was strongly dependent on the choice of substrate material. Films grown on MgO(001) and LaAlO3(001) (pseudocubic indices) substrates are nominally c‐axis oriented; however, the PbTiO3 grains in the film form a fourfold domain structure, with the grains tilted ∼0.6° and ∼0.7°, respectively, toward the [100] directions (cubic or pseudo‐cubic) of the substrates. In addition, these films contain a significant volume fraction of 90°‐domain (a‐axis) stru...
TL;DR: In this paper, the authors reported NMR spin-lattice relaxation rates 1/${\mathit{T}}_{1}$ and Knight shifts 1/${K}$ in the quasi-two-dimensional organic superconductor.
Abstract: The authors report $^{13}\mathrm{C}$ NMR spin-lattice relaxation rates 1/${\mathit{T}}_{1}$ and Knight shifts ${\mathit{K}}_{\mathit{S}}$ in the quasi-two-dimensional organic superconductor \ensuremath{\kappa}-(ET${)}_{2}$Cu[N(CN${)}_{2}$]Br (${\mathit{T}}_{\mathit{c}}$=11.6 K), for an aligned single crystal. The normal-state behavior is reminiscent of the high-${\mathit{T}}_{\mathit{c}}$ cuprates, in which antiferromagnetic fluctuations and spin-gap behavior dominate. In the superconducting state, the data rule out the BCS electron-phonon mechanism as the source of the superconductivity, but support an unconventional pairing state with possible nodes in the gap function.
TL;DR: The gap is large in the vicinity of the {ital M}{ovr bar} is along the (Cu-O bond), and small along the {Gamma}-{ital X} and{ital Y} directions, however, the gap is not zero along these directions, but, within the authors' accuracy, becomes zero about 10{degree} on either side of the ({pi},{pi}) directions.
Abstract: We measure the momentm dependence of the superconducting gap along the Fermi surface of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ by high resolution angle-resolved photoemission spectroscopy. The gap is large in the vicinity of the $\overline{M}$ point (where $\ensuremath{\gamma}$- $\overline{M}$ is along the Cu-O bond), and small along the $\ensuremath{\gamma}$- $X$ and $\ensuremath{\gamma}$- $Y(\ensuremath{\pi},\ensuremath{\pi})$ directions. However, the gap is not zero along these directions, but, within our accuracy, becomes zero about ${10}^{\ensuremath{\circ}}$ on either side of the $(\ensuremath{\pi},\ensuremath{\pi})$ directions. We discuss the implications of these results for the symmetry of the order parameter.