Scanning Tunneling Spectroscopic Studies of the Low-Energy Quasiparticle Excitations in Cuprate Superconductors

We report scanning tunneling spectroscopic (STS) studies of the low-energy quasiparticle excitations of cuprate superconductors as a function of magnetic field and doping level. Our studies suggest that the origin of the pseudogap (PG) is associated with competing orders (COs), and that the occurrence (absence) of PG above the superconducting (SC) transition T _c is associated with a CO energy Δ _CO larger (smaller) than the SC gap Δ _SC. Moreover, the spatial homogeneity of Δ _SC and Δ _CO depends on the type of disorder in different cuprates: For optimally and under-doped YBa₂Cu₃O_7?δ (Y-123), we find that Δ _SC<Δ _CO and that both Δ _SC and Δ _CO exhibit long-range spatial homogeneity, in contrast to the highly inhomogeneous STS in Bi₂Sr₂CaCu₂O_8+x (Bi-2212). We attribute this contrast to the stoichiometric cations and ordered apical oxygen in Y-123, which differs from the non-stoichiometric Bi-to-Sr ratio in Bi-2212 with disordered Sr and apical oxygen in the SrO planes. For Ca-doped Y-123, the substitution of Y by Ca contributes to excess holes and disorder in the CuO₂ planes, giving rise to increasing inhomogeneity, decreasing Δ _SC and Δ _CO, and a suppressed vortex-solid phase. For electron-type cuprate Sr_0.9La_0.1CuO₂ (La-112), the homogeneous Δ _SC and Δ _CO distributions may be attributed to stoichiometric cations and the absence of apical oxygen, with Δ _CO<Δ _SC revealed only inside the vortex cores. Finally, the vortex-core radius (ξ _halo) in electron-type cuprates is comparable to the SC coherence length ξ _SC, whereas ξ _halo～10ξ _SC in hole-type cuprates, suggesting that ξ _halo may be correlated with the CO strength. The vortex-state irreversibility line in the magnetic field versus temperature phase diagram also reveals doping dependence, indicating the relevance of competing orders to vortex pinning.     

Study of capillary interaction between two grains: a new experimental device with suction control

We investigated the behavior of a water liquid bridge formed between two grains. We mainly focused on tensile tests with suction control (capillary pressure). Theoretical and experimental studies are compared. A new experimental device involving suction control of the liquid bridge was developed specifically for this kind of test. Most of the liquid bridge variables and characteristics were measured by image analysis (gorge radius, volume, contact angles, filling angles). Capillary force was measured by differential weighting. Experimental conditions allows us to avoid viscous effects. Our experimental results were close to Young-Laplace equation solutions. The “gorge method”, commonly used for calculating the capillary force, was also validated by our experiments. Liquid bridge rupture was studied and a new rupture criterion is proposed. This criterion depends on the grain radius, contact angle, surface tension and suction and was in agreement with the experimental results.     

Infrared Lock-in Thermography Crack Localization on Metallic Surfaces for Industrial Diagnosis

Optical lock-in thermography with a modulated laser excitation is used for the qualitative assessment of surface cracks in metallic samples. In order to identify and localize an open defect, a novel dedicated image processing of the recorded IR amplitude sequence is proposed. The obtained results demonstrate the potentiality of active lock-in thermography as a contactless measurement tool for the localization of breaking cracks located into specific regions difficult to reach by other conventional non-destructive testing (NDT) techniques such as eddy currents or ultrasound techniques. Crack localization without a prior preparation of the inspected surface can be a possible alternative to penetrant inspection in industrial processes. Various applications illustrating the proposed procedure are presented.     

Evolution of grain structure in deformed metal-polymer laminates

The paper examines the roughening along a metal-polymer interface, to find out whether the relevant length scale is on a sub-grain level or on the grain-size level. This is relevant for understanding the possible delamination of a polymer coating on a metallic substrate. Therefore we have investigated the local lattice orientation in heavily strained ferritic steel using electron back-scatter diffraction. From that data we have calculated the components of the local orientation gradient tensor as well as the local Schmid factor for deformation along [100] and [001] on {101} and {112} slip systems. The curvature of the draw-and-redraw steel- polyethylene terephthalate (PET) laminate interface as well as the curvature of the underlying steel lattice was examined in detail. It is concluded that roughening at a sub-grain length scale along the interface is due to plasticity in the interior of the grains.     

Study on coupling and coupling correction for the SOLEIL ring

One main figure of merit of 3rd generation synchrotron radiation sources is the brilliance of the emitted light. In the presence of magnetic errors, this brilliance is spoiled when the coupling factor, defined as the ratio between the vertical and horizontal emittances, is enlarged. To reach the SOLEIL target coupling of 10⁻² and to possibly go further down, we look for a correction strategy aimed at correcting the coupling at the error sources themselves. For this, we study the correction procedure which consists in minimising the vertical dispersion (D_z) together with the Cross-Talk Closed Orbits (CTCOs) i. e. the non-zero vertical closed orbits created by horizontal dipolar correctors. We show that this procedure is quite effective provided we use a sufficient number of correctors, with judicious location. A detailed statistical study will indicate the values expected for SOLEIL coupling before and after correction: a coupling as low as some 10⁻⁴ can be numerically obtained in most error configurations. Furthermore, the relevance of the use of the CTCOs in any corrector distribution will be discussed, and a correction procedure will be given when there are less correctors than the minimum number required. Finally, we demonstrate that the coupling can be precisely controlled between its minimum value and full coupling.     

Ant colony optimization system for a multi-quantitative and qualitative objective job-shop parallel-machine-scheduling problem

This paper addresses a multi-stage job-shop parallel-machine-scheduling problem with an ant colony optimization system developed. The problem is practically important and yet more complex, especially when customer order splitting in multiple lots for the reduction of operation times in each workstation is allowed. It also includes the decisions of the numbers of parallel machines in workstations dynamically scheduled. In addition, this paper also addresses the multiple-objectives scheduling. For the practical concern, in addition to the production (or quantitative) objectives, the marketing (strategic or qualitative) criteria are also considered. A soft constraint thus may be realized from a thus-called qualitatively evaluated order sequence. The soft constraint with the ant colony optimization solution constructs a penalty function for the multiple qualitative objectives and the results of scheduling obtained by ant colony optimization. For this problem, the ant colony optimization components (including the network representation, tabu lists, transition probabilities, and pheromone trail updating) are also developed and adapted for the multiple objectives. The experiment results of parameter design and different problem sizes are provided. The results of a genetic algorithm also developed for the present problem under the developed system concept are also provided, since in the literature the genetic algorithm has also not been explored for the present problem with multiple objectives and order splitting. The results of both solution techniques show the potential usefulness of the system and are comparable, but the ant colony optimization provides a more computationally efficient better result.     

Eutectic reaction and microstructural characteristics of Al (Li)-Mg2Si alloys

Thermal analysis, directional solidification and metallographic techniques were applied to investigate the pseudobinary eutectic reaction process and the microstructural characteristics of Al(Li)-Mg₂Si alloys. It was demonstrated that the eutectic reaction curve for L Al(Li) + Mg₂Si in the Al(Li)-Mg-Si system moves to the Al-rich corner with the increase of Li additions. The pseudobinary eutectic point with the highest melting temperature and null temperature range of solidification ( T) and the ternary eutectic point for L Al(Li) + Mg₂Si + Si all move towards the Si-rich direction. Li additions widen the range of yielding binary eutectic of Al(Li)-Mg₂Si and depress the appearing of ternary eutectic efficiently. Al(Li)-Mg₂Si eutectic alloys have the best aligned structure when the directional solidification occurs with a T = 0. The Mg₂Si phase has a diversity of morphologies such as rod-like, crossed and rooftop-like. These various morphologies has the same preferred growth direction, i.e. [100].     

Superconductivity, Upper Critical Field and Anomalous Normal State in CePd2Si2 Near the Quantum Critical Point

We report resistivity measurements performed on a high quality single crystal of CePd₂Si₂ under hydrostatic pressure. At ambient pressure the de Haas–van Alphen effect has been also studied. Two different frequencies with weak angular dependence were detected with magnetic field lying in the basal plane, while another frequency was found with magnetic field parallel to the tetragonal c axis. Near the critical pressure, P_c27 kbar, where the antiferromagnetic transition vanishes, the normal state resistivity does not follow the usual Fermi-liquid (FL) behavior and is described by a T^1.3 law, while just below P_c, the resistivity shows clearly separated spin wave and electron–electron contributions. At P_c, the FL form of (T) is not restored even at magnetic field up to 6T. The first appearance of superconductivity is observed at P=19 kbar, and the critical temperature increases with pressure up to 27 kbar. The analysis of the upper critical field at P_c shows that the superconducting state is well described by a weak coupling, clean limit model with a slightly anisotropic orbital limit and a strongly anisotropic paramagnetic one.     

Determination of Magnetic and Nuclear Quadrupole Interactions in La@C82 from EPR Linewidth Data

Abstract

From the analysis of the temperature dependence of the EPR line width, an estimate of the anisotropic parts of the dipolar and quadrupolar hyperfine couplings of lanthanum was derived. Furthermore, the rotational correlation time of the nearly spherical molecule was found to deviate considerably from that of the solvent molecules.