Superconductivity under pressure in the Dirac semimetal PdTe2

The Dirac semimetal PdTe$_2$ was recently reported to be a type-I superconductor ($T_c =$1.64 K, $\mu_0 H_c (0) = 13.6$ mT) with unusual superconductivity of the surface sheath. We here report a high-pressure study, $p \leq 2.5$ GPa, of the superconducting phase diagram extracted from ac-susceptibility and transport measurements on single crystalline samples. $T_c (p)$ shows a pronounced non-monotonous variation with a maximum $T_c =$1.91 K around 0.91 GPa, followed by a gradual decrease to 1.27 K at 2.5 GPa. The critical field of bulk superconductivity in the limit $T \rightarrow 0$, $H_c(0,p)$, follows a similar trend and consequently the $H_c(T,p)$-curves under pressure collapse on a single curve: $H_c(T,p)=H_c(0,p)[1-(T/T_c(p))^2]$. Surface superconductivity is robust under pressure as demonstrated by the large superconducting screening signal that persists for applied dc-fields $H_a > H_c$. Surprisingly, for $p \geq 1.41$ GPa the superconducting transition temperature at the surface $T_c^S$ is larger than $T_c$ of the bulk. Therefore surface superconductivity may possibly have a non-trivial nature and is connected to the topological surface states detected by ARPES. We compare the measured pressure variation of $T_c$ with recent results from band structure calculations and discuss the importance of a Van Hove singularity.Comment: manuscript 9 pages with 8 figures + supplemental material 3 pages with 6 figure

Correlation between the indentation properties and microstructure of dissimilar capacitor discharge welded WC-Co/high-speed steel joints

The welding of cemented carbide to tool steel is a challenging task, of scientific and industrial relevance, as it combines the high level of hardness of cemented carbide with the high level of fracture toughness of steel, while reducing the shaping cost and extending the application versatility, as its tribological, toughness, thermal and chemical properties can be optimally harmonised. The already existing joining technologies often impart either insufficient toughness or poor high-temperature strength to a joint to withstand the ever-increasing severe service condition demands. In this paper, a novel capacitor discharge welding (CDW) process is investigated for the case of a butt-joint between a tungsten carbide-cobalt (WC-Co) composite rod and an AISI M35 high-speed steel (HSS) rod. The latter was shaped with a conical-ended projection to promote a high current concentration and heat at the welding zone. CDW functions by combining a direct current (DC) electric current pulse and external uniaxial pressure after a preloading step, in which only uniaxial pressure is applied. The relatively high heating and cooling rates promote a thin layer of a characteristic ultrafine microstructure that combines high strength and toughness. Morphological analysis showed that the CDW process: (a) forms a sound and net shaped joint, (b) preserves the sub-micrometric grain structure of the original WC-Co composite base materials, via a transitional layer, (c) refines the microstructure of the original martensite of the HSS base material, and (d) results in an improved corrosion resistance across a 1-mm thick layer near the weld interface on the steel side. A nano-indentation test survey determined: (e) no hardness deterioration on the HSS side of the weld zone, although (f) a slight decrease in hardness was observed across the transitional layer on the composite side. Furthermore, (g) an indication of toughness of the joint was perceived as the size of the crack induced by processing the residual stress after sample preparation was unaltered

Dactylospora anziae, a new lichenicolous ascomycete on Anzia from East Asia

Dactylospora anziae growing on species of Anzia is described from Russia and Japan

Rate- and State-Dependent Friction Law and Statistical Properties of Earthquakes

In order to clarify how the statistical properties of earthquakes depend on the constitutive law characterizing the stick-slip dynamics, we make an extensive numerical simulation of the one-dimensional spring-block model with the rate- and state-dependent friction law. Both the magnitude distribution and the recurrence-time distribution are studied with varying the constitutive parameters characterizing the model. While a continuous spectrum of seismic events from smaller to larger magnitudes is obtained, earthquakes described by this model turn out to possess pronounced ``characteristic'' features.Comment: Minor revisions are made in the text and in the figures. Accepted for publication in Europhys. Letter

Determination of the yield radius and yield stress in 2198-T3 aluminum alloy by means of the dual-scale instrumented indentation test

A new dual-scale instrumented indentation test (DualS-IIT) methodology is here proposed to determine the yield stress (in a tensile-like sense). The methodology involves measuring the bulk yield radius, as defined by the expansion cavity model (ECM), induced by a Vickers macro-indentation in a medium plane cross-section. The bulk yield radius is measured by means of a subsurface nano-hardness survey along the load direction in correspondence to the transition interface between the hemispherical strain hardened region and the surrounding elastic region. The methodology has been applied to an Al–Li (A2198-T3) alloy and a yield stress of 297 MPa has been measured (in agreement with a tensile test); moreover, anomalous plastic deformation behaviour has appeared under indentation. The combination of macro- and nano-indentation tests in one single experiment, as in the proposed methodology, offers a unique experimental basis to directly correlate the mechanical properties of a material at two different scales, which at present is an open issue in the research on indentation

Rhodium-catalyzed dehydrogenative borylation of cyclic alkenes

A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki–Miyaura cross-coupling applications are also presented.National Institute of General Medical Sciences (U.S.) (GM-63755

Pressure-induced phase transition of Bi2Te3 into the bcc structure

The pressure-induced phase transition of bismuth telluride, Bi2Te3, has been studied by synchrotron x-ray diffraction measurements at room temperature using a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a high-pressure body-centered cubic (bcc) phase in Bi2Te3 at 25.2 GPa, which is denoted as phase IV, and this phase apperars above 14.5 GPa. Upon releasing the pressure from 29.8 GPa, the diffraction pattern changes with pressure hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc structure can explain the phase IV peaks. We assumed that the structural model of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms are distributed in the bcc-lattice sites with space group Im-3m. The results of Rietveld analysis based on this model agree well with both the experimental data and calculated results. Therefore, the structure of phase IV in Bi2Te3 can be explained by a solid solution with a bcc lattice in the Bi-Te (60 atomic% tellurium) binary system.Comment: 12 pages, 5 figure

Asymptotic displaced charge round impurities in metal crystals with and without surfaces

The displaced charge Δρ at distance r from a localized perturbation V in an inhomogeneous degenerate electron gas may be written in a linear response framework as Δϱ(r) = ∝V(r′)F(rr′)dr′. The response function F is expressed in terms of the Green function of the unperturbed system and attention is then focussed on two cases: * 1. o| * 2. (i) A perfect periodic metal crystal, perturbed by V. * 3. (ii) A metal lattice with a surface in which V is embedded. A full discussion is given of the influence of Fermi surface topology on the anisotropy of Δϱ in the asymptotic region far from the defect. Provided V(r) has certain reasonable properties, it is shown that Δϱ ~ r−nx oscillatory function. For the bulk metal, n can take values between 1 and 5 in different directions for Fermi surfaces with particular topologies. Possible experiments which bear on this anisotropy are briefly referred to. For a planar surface, the displaced charge is shorter range for V embedded in the surface than for the bulk metal, in most, but not all cases. For a closed Fermi surface with non-zero curvature, n = 5 for the parallel configuration

Transmission electron microscopy investigation of separated nucleation and in-situ nucleation in AA7050 aluminium alloy

High resolution transmission electron microscopy (HRTEM) with nanometer-scaled energy-dispersive X-ray (EDX) was employed to investigate the transformation mechanisms of the GP zone → η′ → η precipitation sequence of AA7050, an Al-Zn-Mg-Cu alloy. Serial in-situ HRTEM frames revealed that separated nucleation of an η′ precipitate occurred elsewhere as the adjacent GPII zone dissolved. Evidence from HRTEM coupled with EDX showed that in-situ nucleation of a new η2 precipitate (one form of η) took place, wherein it gradually developed from the original η′ precipitate via a similar hexagonal structure with different compositions. The in-situ transition product was composed of two distinctive regions; one was identified as η′, and the other, as η