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We report on a systematic study of Hall effect using high quality single crystals of type-II Weyl semimetal WTe 2 with the applied magnetic field B//c . The residual resistivity ratio of 1330 and the large magnetoresistance of 1.5 × 10 6 % in 9 T at 2 K, being in the highest class in the literature, attest to their high quality. Based on a simple two-carrier model, the densities ( n e and n h ) and mobilities ( μ e and μ h ) for electron and hole carriers have been uniquely determined combining both Hall- and electrical-resistivity data. The difference between n e and n h is ~ 1% at 2 K, indicating that the system is in an compensated condition. The negative Hall resistivity growing rapidly below ~ 20 K is due to a rapidly increasing μ h /μ e approaching one. Below 3 K in a low field region, we found the Hall resistivity becomes positive, reflecting that μ h /μ e finally exceeds one in this region. These anomalous behaviors of the carrier densities and mobilities might be associated with the existence of a Lifshitz transition and/or the spin texture on the Fermi surface.

Chemical doping effects on structure and superconductivity were studied by introducing Cr at Fe sites in Ba2Ti2Fe2As4O, where Cr2+ can play dual role as impurities and hole dopants. Ba2Ti2(Fe1-xCrx)2As4O (0 ≤ x ≤ 8%) compounds are synthesized by a solid-state reaction and characterized with x-ray diffraction, electric resistivity and magnetization measurements. It is observed that the Cr dopants induce lattice expansion and local structure distortion, and significantly suppress the superconducting transition temperature Tc. In the meantime, the residual resistivity is found steadily increased with Cr doping. Comprehensive analyses show that Tc suppression is strongly correlated with the impurity-induced scattering to electrons, which can be fitted with the Abrikosov-Gor'kov-like scaling function.

Monitoring and delineating the spatial distribution of shale fracturing is fundamentally important to shale gas production. Standard monitoring methods, such as time-lapse seismic, cross-well seismic and micro-seismic methods, are expensive, timeconsuming, and do not show the changes in the formation with time. The resistivities of hydraulic fracturing fluid and reservoir rocks were measured. The results suggest that the injection fluid and consequently the injected reservoir are characterized by very low resistivity and high chargeability. This allows using of the controlled-source electromagnetic method (CSEM) to monitor shale gas hydraulic fracturing. Based on the geoelectrical model which was proposed according to the well-log and seismic data in the test area the change rule of the reacted electrical field was studied to account for the change of shale resistivity, and then the normalized residual resistivity method for time lapse processing was given. The time-domain electromagnetic method (TDEM) was used to continuously monitor the shale gas fracturing at the Fulin shale gas field in southern China. A high-power transmitter and multi-channel transient electromagnetic receiver array were adopted. 9 h time series of Ex component of 224 sites which were laid out on the surface and over three fracturing stages of a horizontal well at 2800 m depth was recorded. After data processing and calculation of the normalized resistivity residuals, the changes in the Ex signal were determined and a dynamic 3D image of the change in resistivity was constructed. This allows modeling the spatial distribution of the fracturing fluid. The model results suggest that TDEM is promising for monitoring hydraulic fracturing of shale.

In this work, the effect of Ca2+ iso-valence substitution for Sr2+ on properties of Bi2Sr1.6La0.4CuO6+δ superconductors is presented. Samples series with nominal composition of Bi2Sr1.6-xCaxLa0.4CuO6+δ (x= 0, 0.2, 0.4, 0.6 and 0.8) are prepared by a solid-state reaction method. When Ca content is increased, the X-ray diffraction technique shows that the cell parameters a and c decrease, while b one is almost constant. The scanning electron microscopy analysis reveals that the substitution has no significant effect on the porosity and the grain size of the samples. The physical properties of the samples are studied by the analysis of the magneto-resistivity curves measured under magnetic fields in the range 0-1 T. As Ca is added, the results show that the high temperature transition appears and is pushed up to 94.87 K for x=0.8. The substitution also improves the bulk onset critical transition temperature, the transition width, the residual resistivity, the activation energy of vortices and the irreversibility field. The best results are seen for x=0.4 of Ca content.

The longitudinal resistivity and anomalous Hall resistivity of 50 nm Co2FeSi films deposited on Si (1 0 0) substrate at different temperatures have been investigated as functions of disorder. The film deposited at 450 °C has minimum disorder and the lowest temperature (Tmin ∼ 11 K) at which resistivity goes through a minimum as a function of temperature. The film with the highest disorder has the largest Tmin, residual resistivity and absolute value of resistivity at any given temperature. The resistivity data have been analyzed taking into account the contributions from electron-electron scattering, electron-phonon scattering and disorder-induced enhanced electron-electron interaction, which dominates at low temperatures. The effect of Tmin is observed in Hall resistivity for all the samples. Anomalous Hall conductivity (AHC) is extremely sensitive to the degree of disorder present in the films and has the value 180 S/cm at 300 K for the most ordered TS450 film, which tallies well with the theoretically calculated value for the Co2FeSi alloy with L21 structure. The influence of disorder on the longitudinal resistivity and anomalous Hall effect has been discussed in detail.

Electrical and thermal transport properties of the Heusler-type alloys, Ru2VAl1−xGax (x = 0.0–1.0) were studied by means of the electrical resistivity, Seebeck coefficient, and thermal conductivity measurements. All studied compounds show weak metallic characteristics with a low residual resistivity ratio. In addition, the Ru2VAl1−xGax alloys with x ≤ 0.75 show an n-type thermoelectric conduction from 10 to 300 K, while Ru2VGa displays p-type conduction. The estimated Fermi energy of these materials is higher than 0.5 eV, endorsing their metallic character. From the thermal conductivity study, we noticed that low-temperature thermal conductivity decreases with increasing Ga content for x ≤ 0.5 and then increases with further Ga substitution. This observation is essentially due to the change in the phonon scattering processes as a result of the substitution of heavier Ga atoms into the Al sites of Ru2VAl. It is important that an enhanced thermoelectric figure of merit ZT was found in Ru2VAl0.25Ga0.75, about seven times higher than that in Ru2VAl.

A model with two channels of electrical transport (TCET) for perovskite manganites is proposed, and it is described by an equivalent device with two current-carrier channels. In one channel, there is a spin-independent resistor (R3) with an equivalent resistivity of ρ3. In the other channel, there are two spin-dependent resistors in series (R1 and R2) with an equivalent resistivity of ρ1 + ρ2. The component ρ1 includes residual resistivity and the resistivity contributed by crystal-lattice scattering. The other component of the equivalent resistivity, ρ2, originates from the spin orientations of the itinerant electrons and the local electrons of the outer O 2p and Mn 3d orbits that deviate from the orientation of their ground states when the test temperature is close to the Curie temperature. Using this model, we fitted the experimental curves of the resistivity versus test temperature for single-crystalline La1−xSrxMnO3 (0.00 ≤ x ≤ 0.40) and polycrystalline La0.6Sr0.4Mn1−xFexO3 (0.00 ≤ x ≤ 0.30). In addition, we investigated the effects of the fraction of the antiferromagnetic phase, scattering at the crystallite interfaces, and the crystal-cell constants on the samples' resistivity. The physical mechanism of the TCET model was explained using an O 2p itinerant-electron model, which has been used in other studies to explain the magnetic ordering of several series of spinel ferrites and perovskite manganites.

Investigations of phase relations in the ternary system Ti-Fe-Sb show that the single-phase region of the Heusler phase is significantly shifted from stoichiometric TiFeSb (reported previously in the literature) to the Fe-rich composition TiFe1.33Sb. This compound also exhibits Fe/Ti substitution according to Ti1+xFe1.33-xSb (-0.17 ≤ x ≤ 0.25 at 800 °C). Its stability, crystal symmetry and site preference were established by using X-ray powder techniques and were backed by DFT calculations. The ab initio modeling revealed TiFe1.375Sb to be the most stable composition and established the mechanisms behind Fe/Ti substitution for the region Ti1+xFe1.33-xSb, and of the Fe/Co substitution within the isopleth TiFe1.33Sb-TiCoSb. The calculated residual resistivity of Ti1+xFe1.33-xSb, as well as of the isopleths TiFe1.33Sb-TiCoSb, TiFe0.665Co0.5Sb-TiCoSb0.75Sn0.25 and TiFe0.33Co0.75Sb-TiCoSb0.75Sn0.25, are in a good correlation with the experimental data. From magnetic measurements and 57Fe Mossbauer spectrometry, a paramagnetic behavior down to 4.2 K was observed for TiFe1.33Sb, with a paramagnetic Curie-Weiss temperature of -8 K and an effective moment of 1.11μB per Fe. Thermoelectric (TE) properties were obtained for the four isopleths Ti1+xFe1.33-xSb, TiFe1.33Sb-TiCoSb, TiFe0.665Co0.5Sb-TiCoSb0.75Sn0.25 and TiFe0.29Co0.78Sb-TiCoSb0.75Sn0.25 by measurements of electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (λ) at temperatures from 300 K to 823 K allowing the calculation of the dimensionless figure of merit (ZT). Although p-type Ti1+xFe1.33-xSb indicates a semi-conducting behavior for the Fe rich composition (x = -0.133), the conductivity changes to a metallic type with increasing Ti content. The highest ZT = 0.3 at 800 K was found for the composition TiFe1.33Sb. The TE performance also increases with Fe/Co substitution and reaches ZT = 0.42 for TiCo0.5Fe0.665Sb. No further increase of the TE performance was observed for the Sb/Sn substituted compounds within the sections TiFe0.665Co0.5Sb-TiCoSb0.75Sn0.25 and TiFe0.33Co0.75Sb-TiCoSb0.75Sn0.25. However, ZT-values could be enhanced by about 12% via the optimization of the preparation route (ball-mill conditions and heat treatments).

Incorporation of the secondary oxide phase into the manganite composite capable of enhancing low-field magnetoresistance (LFMR) for viability in high-performance spintronic applications. Polycrystalline La0.67Ca0.33MnO3 (LCMO) was prepared via the sol–gel route in this study. The structural, microstructural, magnetic, electrical, and magneto-transport properties of (1−x) LCMO: x NiO, x = 0.00, 0.05, 0.10, 0.15 and 0.20 were investigated in detail. The X-ray diffraction (XRD) patterns showed the coexistence of LCMO and NiO in the composites. The microstructural analysis indicated the amount of NiO nanoparticles segregated at the grain boundaries or on the surface of LCMO grains increased with the increasing secondary phase content. LCMO and NiO still retained their individual magnetic phase as observed from AC susceptibility (ACS) measurement. This further confirmed that there is no interfacial diffusion reaction between these two compounds. The NiO nanoparticle acted as a barrier to charge transport and caused an increase in resistivity for composite samples. The residual resistivity due to the grain/domain boundary is responsible for the scattering mechanism in the metallic region as suggested by the theoretical model fitting, ρ(T)=ρ0+ρ2T2+ρ4.5T4.5. The magnetoresistance values of LCMO and its composites were found to increase monotonically with the decrease in temperature. Hence, the LFMR was observed. Nonetheless, the slight reduction of LFMR in composites was attributed to the thick boundary layer created by NiO and impaired the spin polarised tunnelling process.

In this work, we have investigated structural, transport, magnetic, magnetocaloric (MC) properties and critical exponents analysis of the (Ni 2.1− x Co x )Mn 0.9 Ga ( x = 0, 0.04, 0.12 and 0.2) Heusler alloys. For all compositions, cubic austenite (A) phase with metallic character is observed at room temperature (RT). With increasing of Co content, magnitude of resistivity decreases, whereas residual resistivity ( ρ 0 ) and electron scattering factor ( A ) increases linearly. Magnetic measurements exhibit that ferromagnetic (FM) Curie temperature ( T C A ) increases towards RT by increasing Co concentration. All samples show conventional MC and maximum magnetic entropy change (Δ S M peak ) of −2.8 Jkg −1 K −1 is observed for x = 0.12 at 147 K under 5 T. Further, hysteresis is observed between cooling and warming cycles around FM-PM ( T C A ) transition in x = 0, 0.04 samples, which suggests that first order nature of transition. However, there is no hysteresis across T C A for x = 0.12 and 0.2 samples suggesting second-order nature of the transition. The critical exponents are calculated for x = 0.12 sample around T C A using Arrott plot and Kouvel-Fisher method, the estimated critical exponents are found closer to the mean-field model reveals the long range ferromagnetic ordering in this composition.

Temperature dependences of the basal-plane electrical resistance of underdoped YBa 2 Cu 3 O t − δ single crystals are investigated in a broad temperature range down to the superconducting transition, after a fast cooldown from 650 ° C as well as after a room-temperature annealing. A stepped behavior of the superconducting transition has been observed, pointing to an inhomogeneity of the samples. Annealing has been revealed to lead to a narrowing of the superconducting transition and a reduction of both, the residual resistivity and the phonon scattering coefficient. This is accompanied by a slight increase of the Debye temperature attributed to a decrease of the lattice parameter caused, in turn, by a redistribution of the labile oxygen. The revealed changes of the parameters of the temperature dependence of the electrical resistance point to an equalization of the concentration of the labile oxygen in the layers and its ordering.

Soil discharge occurs when it is subjected to high impulse current, and it is closely associated with the impulse performance of grounding systems. In this paper, a new method is put forward to visualize the inner impulse discharge region of simulate soil (fine sand) directly, using X-ray imaging technology. According to the three views of the discharge region, the boundary surface of the discharge region can be obtained based on image filtering and edge extraction by 3-D reconstruction. On this basis, the ionization parameters (i.e., the residual resistivity of soil discharge region $\rho_{res}$ and the critical breakdown electric-field strength $E_c$ ) are calculated by a finite-element method. The results show that discharge region volume enlarges with water content increasing, and $\rho_{res}$ is approximately equal to 0.001%–0.003% of the original soil resistivity $\rho_{0}$ . $E_c$ increases from 100 to 150 kV/m, as soil water content decreases from 5% to 2%.

We investigate a unique material system, Ba0.6K0.4Fe2As2 thin film, using the optical spectroscopic technique. The Ba0.6K0.4Fe2As2 thin film was prepared on an Al2O3 (0001) substrate using the pulsed laser deposition (PLD) method and a subsequent post-annealing process. The Ba0.6K0.4Fe2As2 thin film sample shows a much larger residual resistivity as compared to that of a single crystal of the same compound. We applied the well-known multilayer thin film analysis to obtain optical constants of Ba0.6K0.4Fe2As2 thin film layer from the measured reflectance spectra of the Ba0.6K0.4Fe2As2/Al2O3 sample. The overall temperature-dependent optical properties were found to be similar to those of a corresponding single crystal. From our analysis, we also roughly estimated the superfluid density of 3860 cm−1 and the corresponding London penetration depth of 412 nm of the Ba0.6K0.4Fe2As2 thin film. Our results indicate that this Ba0.6K0.4Fe2As2 thin film prepared by PLD does retain some of the intrinsic physical properties of single crystal samples.

The quadrupole and dipole magnets for the high-luminosity large hadron collider (HL-LHC) upgrade will be based on Nb 3 Sn Rutherford cables that operate at 1.9 K and experience magnetic fields of up to about 12 T. An important step in the design of these magnets is the development of the high-aspect-ratio Nb 3 Sn cables to achieve the nominal field with sufficient margin. The strong plastic deformation of unreacted Nb 3 Sn strands during the Rutherford cabling process may induce non-negligible I c and Residual Resistivity Ratio degradation. In this paper, the cabling degradation is investigated as a function of the cable geometry for both Powder-in-Tube and Restack Rod Process conductors. Based on this analysis, new baseline geometries for both 11 T and quadrupole magnets of HL-LHC are proposed.

The multiple solutions of conduction and vapor cooled copper leads modeling current delivery to a superconducting magnet have been numerically calculated. Both ideal convection and convection with a finite heat transfer coefficient for an imposed coolant mass flow rate have been considered. Because of the nonlinearities introduced by the temperature dependent material properties, two solutions exist, one stable and one unstable regardless of the cooling method. The limit points separating the stable form the unstable steady states form the blow-up threshold beyond which, any further increase in the operating current results in a thermal runway. An interesting finding is that the multiplicity persists even when the cold end temperature is raised above the liquid nitrogen temperature. The effect of various parameters such as the residual resistivity ratio, the overcurrent and the variable conductor cross section on the bifurcation structure and their stabilization effect on the blow-up threshold is also evaluated.

We report the observation of quantum Hall effect (QHE) in a Bi 2 Se 3 single crystal having carrier concentration ( n ) ∼ 1.13 × 10 19 cm −3 , three dimensional Fermi surface and bulk transport characteristics. The plateaus in Hall resistivity coincide with minima of Shubnikov de Haas oscillations in resistivity. Our results demonstrate that the presence of perfect two dimensional transport is not an essential condition for QHE in Bi 2 Se 3 . The results of high resolution X-ray diffraction (HRXRD), energy-dispersive X-ray spectroscopy (EDX), and residual resistivity measurements show the presence of enhanced crystalline defects and microstrain. We discuss the possible origin of the observed QHE and correlate its existence to the crystalline defects.

Potassium tungsten bronzes $$\hbox {K}_{x}\hbox {WO}_{3}$$ ( $$x=0.20$$ and 0.22) with the coexistence of charge density wave (CDW) and superconductivity (SC) were prepared from $$\hbox {K}_{2}\hbox {WO}_{4},\, \hbox {WO}_{3}$$ and W powders using a hybrid microwave method. The structure refinement confirmed that all samples had a pure hexagonal phase with the space group of $$P6_{3}$$ /mcm. The distortion degree of W–O octahedron declines with x and is independent of synthesis condition for the same x (=0.20). The CDW transition is studied as a function of residual resistivity ratio. By increasing the crystallinity of sample, this transition can be suppressed, which is probably attributed to the interaction between CDW and defects in crystallites. The CDW transition temperature increases with x, which may be related to the decline of the distortion degree of W–O octahedron. The competition between CDW and SC is observed according to the resistivity and magnetization measurements.

The effect of the Ni/Cu substitution on the electrical resistivity and microstructure of the polycrystalline GdNi5–xCux series was studied. The value of temperature of phase transition (Tph) estimated from temperature dependence of electrical resistance varied non-linearly across copper doping from 32.5 K (x=0.0) to 29.1 K (x=5.0). The value of residual resistivity (ρo) estimated at low temperature range decreased from 27.28 μΩcm (x=0.0) to 9.44 μΩcm (x=5.0), which was discussed as the influence of microstructure. In order to describe the temperature dependence of resistivity ρ(T) a variety of approaches were applied due to different scattering mechanisms occurring at high and low temperature ranges. The change within ρ(T) curvature was evidenced at low temperature range across copper doping. The temperature variation of the resistivity was quite peculiar for Cu-rich compounds (x=4.8, x=5.0), which might be correlated with the incommensurate magnetic structure derived from the weakly negative interaction between the nearest neighbours of Gd. The correlation between microstructure and resistivity was observed.

Polar metals are an intriguing class of materials that simultaneously host free carriers and polar structural distortions. Despite the name "polar metal," however, most well-studied polar metals are poor electrical conductors. Here, we demonstrate the molecular beam epitaxial (MBE) growth of LaPtSb and LaAuGe, two polar metal compounds whose electrical resistivity is an order of magnitude lower than the well studied oxide polar metals. These materials belong to a broad family of $ABC$ intermetallics adopting the stuffed wurtzite structure, also known as hexagonal Heusler compounds. Scanning transmission electron microscopy (STEM) reveals a polar structure with unidirectionally buckled $BC$ (PtSb, AuGe) planes. Magnetotransport measurements demonstrate good metallic behavior with low residual resistivity ($\rho_{LaAuGe}=59.05$ $\mu\Omega\cdot$cm and $\rho_{LaAPtSb}=27.81$ $\mu\Omega\cdot$cm at 2K) and high carrier density ($n_h\sim 10^{21}$ cm$^{-3}$). Photoemission spectroscopy measurements confirm the band metallicity and are in quantitative agreement with density functional theory (DFT) calculations. Through DFT-Chemical Pressure and Crystal Orbital Hamilton Population analyses, the atomic packing factor is found to support the polar buckling of the structure, though the degree of direct interlayer $B-C$ bonding is limited by repulsion at the $A-C$ contacts. When combined with insulating hexagonal Heuslers, these materials provide a new platform for fully epitaxial, multiferroic heterostructures.

The ground states of bosons have been classified into superfluid, Mott insulator, and bose glass. Recent experiments in two-dimensional superconductors strongly suggest the existence of the fourth quantum state of Cooper pairs, i.e., bose metal or quantum metal, where the resistivity remains constant at lowest temperature. However, its theoretical understanding remains unsettled. In this paper, we show theoretically that the bosons in the dilute limit subject to dissipation can lose the superfluidity and remain metallic, utilizing the Feynman's picture of superfluidity in the first quantized formulation. This result is relevant to the quantum vortices under an external magnetic field in two-dimensional superconductors with the finite resistivity of the normal core as the source of dissipation., 5+2 pages, 4+3 figures; v2: added references and clarified the difference from previous study

Most interesting examples of violations of the Mott-Ioffe-Regel (MIR) resistivity limit are found in materials with strong electronic correlations that are not well understood by theory. We demonstrate that first principles theory can predict the experimentally observed frequency dependence of the optical conductivity for a novel class of metals where the residual resistivity is near or above the MIR limit, which we define as a ``bad metal.'' The predicted optical conductivity of a NiCoCr alloy is in good agreement with experiment. It is demonstrated that the width of the Drude peak describing the low-frequency part of optical conductivity is comparable to the Fermi energy. The latter, together with a mean free path comparable to the interatomic distance, indicates the absence of well-defined quasiparticles. In contrast to traditional bad metals with strong electron-electron interactions, both the high resistivity and the large width of the Drude peak in these alloys result from strong scattering on disordered atomic potentials that can be understood using modern density functionals.

We study the quantum phase transitions in the nickel pnctides, CeNi2−δ(As1−xPx)2 (δ ≈ 0.07–0.22) polycrystalline samples. This series displays the distinct heavy fermion behavior in the rarely studied parameter regime of dilute carrier limit. We systematically investigate the magnetization, specific heat and electrical transport down to low temperatures. Upon increasing the P-content, the antiferromagnetic order of the Ce-4f moment is suppressed continuously and vanishes at xc ~ 0.55. At this doping, the temperature dependences of the specific heat and longitudinal resistivity display non-Fermi liquid behavior. Both the residual resistivity ρ0 and the Sommerfeld coefficient γ0 are sharply peaked around xc. When the P-content reaches close to 100%, we observe a clear low-temperature crossover into the Fermi liquid regime. In contrast to what happens in the parent compound x = 0.0 as a function of pressure, we find a surprising result that the non-Fermi liquid behavior persists over a nonzero range of doping concentration, xc x 2−δ(As1−xPx)2 in comparison with those of its 1111 counterpart, CeNi(As1−xPx)O. Our results indicate a non-Fermi liquid phase in the global phase diagram of heavy fermion metals.

The high-entropy alloys Al$_{x}$CrFeCoNi exist over a broad range of Al concentrations ($0 < x < 2$). With increasing Al content their structure is changed from the fcc to bcc phase. We investigate the effect of such structural changes on transport properties including the residual resistivity and the anomalous Hall resistivity. We have performed a detailed comparison of the first-principles simulations with available experimental data. We show that the calculated residual resistivities for all studied alloy compositions are in a fair agreement with available experimental data as concerns both the resistivity values and concentration trends. We emphasize that a good agreement with experiment was obtained also for the anomalous Hall resistivity. We have completed study by estimation of the anisotropic magnetoresistance, spin-disorder resistivity, and Gilbert damping. The obtained results prove that the main scattering mechanism is due to the intrinsic chemical disorder whereas the effect of spin polarization on the residual resistivity is appreciably weaker., 8 pages, 3 figures, accepted in Phys. Rev. B

The strain irreversibility cliff (SIC), marking the abrupt change of the intrinsic irreversible strain limit εirr,0 as a function of heat-treatment (HT) temperature θ in Nb3Sn superconducting wires made by the restacked-rod process (RRP®), is confirmed in various wire designs. It adds to the complexity of reconciling conflicting requirements on conductors for fabricating magnets. Those intended for the high-luminosity upgrade of the Large Hardon Collider (LHC) at the European Organization for Nuclear Research (CERN) facility require maintaining the residual resistivity ratio RRR of conductors above 150 to ensure stability of magnets against quenching. This benchmark may compromise the conductors’ mechanical integrity if their εirr,0 is within or at the bottom of SIC. In this coupled investigation of strain and RRR properties to fully assess the implications of SIC, we introduce an electro-mechanical stability criterion that takes into account both aspects. For standard-Sn billets, this requires a strikingly narrow HT temperature window that is impractical. On the other hand, reduced-Sn billets offer a significantly wider choice of θ, not only for ensuring that εirr,0 is located at the SIC plateau while RRR ≥ 150, but also for containing the strain-induced irreversible degradation of the conductor’s critical-current beyond εirr,0. This study suggests that HT of LHC magnets, made of reduced-Sn wires having a Nb/Sn ratio of 3.6 and 108/127 restacking architecture, be operated at θ in the range of 680 to 695 °C (when the dwell time is 48 hours).

Electrical transport properties near an electronic Ising-nematic quantum critical point in two dimensions are of both theoretical and experimental interest. In this work, we derive a kinetic equation valid in a broad regime near the quantum critical point using the memory matrix approach. The formalism is applied to study the effect of the critical fluctuations on the dc resistivity through different scattering mechanisms, including umklapp, impurity scattering, and electron-hole scattering in a compensated metal. We show that electrical transport in the quantum critical regime exhibits a rich behavior that depends sensitively on the scattering mechanism and the band structure. In the case of a single large Fermi surface, the resistivity due to umklapp scattering crosses over from $\rho\sim T^2$ at low temperature to sublinear at high temperature. The crossover temperature scales as $q_0^3$, where $q_0$ is the minimal wavevector for umklapp scattering. Impurity scattering leads to $\rho-\rho_0\sim T^\alpha$ ($\rho_0$ being the residual resistivity), where $\alpha$ is either larger than 2 if there is only a single Fermi sheet present, or 4/3 in the case of multiple Fermi sheets. Finally, in a perfectly compensated metal with an equal density of electrons and holes, the low temperature behavior depends strongly on the structure of "cold spots" on the Fermi surface, where the coupling between the quasiparticles and order parameter fluctuations vanishes by symmetry. In particular, for a system where cold spots are present on some (but not all) Fermi sheets, $\rho\sim T^{5/3}$. At higher temperatures there is a broad crossover regime where $\rho$ either saturates or $\rho\sim T$, depending on microscopic details. We discuss these results in the context of recent quantum Monte Carlo simulations of a metallic Ising nematic critical point, and experiments in certain iron-based superconductors., Comment: 11 pages main text, 19 pages appendix, 13 figures

We report the single crystal growth and characterization of crystalline topological insulator SnTe with XRD, SEM, EDX and resistivity measurements. We have grown SnTe single crystal by modified Bridgman method. X-ray diffraction analysis shows the orientation of the cleaved sample along {200} reflections showing the single crystalline nature of our crystal. Single β-SnTe phase was confirmed from the Rietveld refinement of room temperature-powder XRD pattern. Scanning Electron Microscopy (SEM) image shows flat terraces demonstrating a layered structure in SnTe single crystal. Energy Dispersive X-ray spectroscopy (EDX) on different regions of same crystal showsnearly1:1 stoichiometry throughout the grown crystal. Zero field transport measurements on (200) plane shows a clear metallic behavior down to 2K having the residual resistivity ratio (RRR) ∼6.8. The hump in temperature derivative of resistivity curve at ∼60K indicates the transition due to Teantisite defects.

This multidisciplinary study paves way to investigate the crucial of fundamental characteristic properties including the bulk density, electrical, superconducting, flux pinning mechanism, crystal structure quality and strength quality of interaction between the superconducting grains in the Bi(2.1)Sr(2.0)Ca(1.1)Cu(2.0)Oy (Bi-2212) superconducting materials with the partial replacement of gallium foreign impurity by bismuth nanoparticles in the crystal structure. Characterizations of polycrystalline ceramic materials prepared by standard ceramic route in the atmospheric air are performed by means of conventional experimental measurement methods such as powder X-ray diffraction, Archimedes water displacement, dc electrical resistivity versus temperature and critical current density examinations. All the bulk Bi-site Ga partial replaced materials exhibit the Bi-2212 superconducting phase within the different fraction levels (%73.1 -94.8), moderate self-field critical current densities 54-96 A/cm(2) and wide-ranging offset and onset critical transition temperature range of 45.65 K-84.52 K and 70.06 K-85.00 K. As for the experimental findings of bulk density and related degrees of granularity (porosity) parameters, the bulk density parameter is found to be between 5.76 g/cm(3) and 6.12 g/cm(3) when the corresponding residual porosity value is also obtained to be in a range of 8.57 % -2.86%. Moreover, the mobile hole carrier concentrations in the short-range-ordered antiferromagnetic Cu-O-2 layers are found to be in the range from 0.085 until 0.152. Additionally, the role of Ga/Bi partial substitution in the crystal lattice on the normal state resistivity, residual resistivity, residual resistivity ratio, vibrational mode intensities, texturing, superconducting volume fractions, mobile hole carrier concentrations, average crystallite sizes, Lotgering indices and cell parameters are discussed in details. All the experimental results and theoretical approaches show that the characteristic properties tend to improve regularly with the increment in the Ga foreign impurity level until x = 0.05 due to the increment in the crystal structure quality and interaction between the superconducting grains. After the critical Ga/Bi substitution level of x = 0.05, every feature degrades considerably. (C) 2018 Elsevier B.V. All rights reserved. https://doi.org/10.1016/j.jallcom.2018.09.071

The electronic conduction mechanism in (La0.7Ba0.3MnO3)1-x (BaTiO3)x (x = 0.05) compound have been studied. The structure and phase purity of sample have been characterized using XRD technique. The diffraction pattern is explained on the basis of double phase Rietveld refinement and the calculated structural parameters of both the two phases are determined. It is observed that BaTiO3 significantly shifts the TMI temperature below the room temperature. The conduction mechanism has been analyzed for T

We have investigated the structural, transport properties and electronic structure of CaIrO3 (CIO) thin film on (LaAlO3)0.3(Sr2AlTaO6)0.7 (100) substrate. X-ray diffraction results reveal the phase purity and the epitaxial growth of the film with partial tensile strain. The overall behavior of the temperature dependent electrical resistivity is insulating like whereas residual resistivity ratio indicates that the semi-metallic like transport in the CIO thin film. The semi-metallic nature was further confirmed by x-ray photoemission spectroscopy (XPS) from the observation of screening mechanism present in Ir 4f state and finite density of states at the Fermi level.

FeSn is a room-temperature antiferromagnet expected to host Dirac fermions in its electronic structure. The interplay of magnetic degree of freedom and the Dirac fermions makes FeSn an attractive platform for spintronics and electronic devices. While stabilization of thin film FeSn is needed for the development of such devices, there exist no previous report of epitaxial growth of single crystalline FeSn. Here we report the realization of epitaxial thin films of FeSn (001) grown by molecular beam epitaxy on single crystal SrTiO$_{3}$ (111) substrates. By combining X-ray diffraction, electrical transport, and torque magnetometry measurements, we demonstrate the high quality of these films with the residual resistivity ratio $\rho_{xx}(300 \hspace{0.2em}{\rm K})/\rho_{xx}(2 \hspace{0.2em}{\rm K}) = 24$ and antiferromagnetic ordering at $T_{\rm N}$ = 353 K. These developments open a pathway to manipulate the Dirac fermions in FeSn by both magnetic interactions and the electronic field effect for use in antiferromagnetic spintronics devices.

We report a study on the thermal conductivity (κ) of two as-cast vanadium samples having different residual resistivity ratios (RRR). The sample having higher RRR shows a distinct peak near 38 K in the temperature (T) dependence of κ, whereas no such behavior is observed in the sample with smaller RRR. However, the κ of both the samples tend to saturate near the room temperature at about 30 W/m K, which is nearly one order less than that pure copper. We found that even for vanadium with a very high RRR (1524), the κ(300 K) is nearly same (34 W/m K) as that of the highly disordered samples. We found that while the κ at low T is strongly dependent on the amount of disorder present, we argue that the difference between the κ of vanadium and copper near room temperature is not due to the presence of disorder. Rather it is due to the intrinsic effects, such as s-d interband scattering, spin fluctuations etc., present in vanadium.

The high-entropy alloys AlxCrFeCoNi exist over a broad range of Al concentrations (0 < x < 2). With increasing Al contenttheir structure is changed from the fcc to bcc phase. We investigate the effect of such structural changes on transport propertiesincluding the residual resistivity, the anisotropic magnetoresistance, and the anomalous Hall resistivity. We have performeda detailed comparison of the first-principles simulations with available experimental data. We show that the calculated residualresistivity of the bcc phase is in a perfect agreement with experiment for all studied alloy compositions, whereas there are significantadditional non-intrinsic electron scattering channels in the fcc phase. We argue that the combination of the modern alloy-specificab initio methods for calculations of transport properties and experimental measurements might serve as an additional importanttool for the sample characterization of high-entropy alloys.

Here we report the single crystal growth, characterization, magneto-transport and magnetization studies of NbAs2 semimetal. The zero field resistivity vs temperature shows metallic behaviour with large residual resistivity ratio. Field measurements show an upturn in resistivity at low temperatures and subsequent saturation. The transverse magneto-resistance reveals a large unsaturated MR reaching 1.1 x 105 % at 2.5 K and a field of 14 T with Shubnikov de Haas oscillations. Kohler’s rule analysis suggests same scattering mechanism operating across the temperature regime from 300 K down to 2.5 K except at very low MR region indicating the role of a critical field. The absence of negative magneto-resistance in the longitudinal measurement points out that NbAs2 is not a conventional Weyl semimetal. The non-linear Hall resistance behavior evinces the presence of multiple carriers in the system. The de Haas van Alphen oscillations in the magnetization measurement display anisotropy with respect to the crystalline direction.

The recent discovery of Dirac and Weyl semimetals (WSM) promises novel transport properties with exceptional magneto-resistance. We have grown high quality single crystals of one of the candidate compound TaP using iodine vapour transport method. We further carried out magnetotransport measurement in temperature regime 5 K to 300 K. The residual resistivity ratio (RRR) is around 11, implying high quality of our single crystal. TaP exhibits linear magneto-resistance 2.31×104 % at 5 K and 125 % at room temperature in a magnetic field of 6 T. Our results imply TaP is a confirmed Weyl semimetal and that can host elusive Majorana fermions.

Materials informatics exploiting machine learning techniques, e.g., Bayesian optimization (BO), have the potential to reduce the number of thin-film growth runs for optimization of thin-film growth conditions through incremental updates of machine learning models in accordance with newly measured data. Here, we demonstrated BO-based molecular beam epitaxy (MBE) of SrRuO3, one of the most intensively studied materials in the research field of oxide electronics, mainly owing to its unique nature as a ferromagnetic metal. To simplify the intricate search space of entangled growth conditions, we ran the BO for a single condition while keeping the other conditions fixed. As a result, high-crystalline-quality SrRuO3 film exhibiting a high residual resistivity ratio of over 50 as well as strong perpendicular magnetic anisotropy was developed in only 24 MBE growth runs in which the Ru flux rate, growth temperature, and O3-nozzle-to-substrate distance were optimized. Our BO-based search method provides an efficient experimental design that is not as dependent on the experience and skills of individual researchers, and it reduces experimental time and cost, which will accelerate materials research.

Magnetic ($\chi$), transport ($\rho$) and heat capacity ($C_m$)properties of CeIrSi are investigated to elucidate the effect of geometric frustration in this compound with trillium type structure because, notwithstanding its robust effective moment, $\mu_{\rm eff}\approx 2.46\mu_B$, this Ce-lattice compound does not undergo a magnetic transition. In spite of that it shows broad $C_m(T)/T$ and $\chi(T)$ maxima centered at $T_{max}\approx 1.5$\,K, while a $\rho \propto T^2$ thermal dependence, characteristic of electronic spin coherent fluctuations, is observed below $T_{coh} \approx 2.5$\,K. Magnetic field does not affect significantly the position of the mentioned maxima up to $\approx 1$\,T, though $\chi(T)$ shows an incipient structure that completely vanishes at $\mu_0 H \approx 1$\,T. Concerning the $\rho \propto T^2$ dependence, it is practically not affected by magnetic field up to $\mu_0 H = 9$\,T, with the residual resistivity $\rho_0(H)$ slightly decreasing and $T_{coh}(H)$ increasing. These results are compared with the physical properties observed in other frustrated intermetallic compounds, Comment: 8 pages, 7 figures

The improved mechanical properties of the Ni-alloy reinforced Bi 2-x Pb x Sr 2 Ca 2 Cu 3 O 10-x (Bi-2223)-released on 2016 by the Sumitomo Electric Industries, Osaka, Japan, (HT-NX type)-renewed the interest on this material for high-field applications. Whether Bi-2223 can be preferred to other high-temperature superconductors for very-high-field magnets depends also on the solutions found to protect the coil in the case of quenches. A comprehensive study of the quench propagation requires information about the temperature and field dependence of the critical current (I C ), the thermal conductivity (κ) of the conductor, and the electrical resistivity of the normal matrix (ρ norm ). Most of these data are unavailable in the literature for the HT-NX tape. This paper intends to fill this gap, reporting the results of an extensive measurement campaign of its electrical and thermo-physical properties. We have found that I C decreases linearly with T in the investigated range of fields 1-19 T. The well-known magnetic hysteresis of I C (B) has been examined in detail. We have observed that the value of I C at a given field varies upon repeated I-V measurements, with a consequent reduction of the hysteresis amplitude. The longitudinal κ has been investigated in magnetic fields up to 19 T. ρ norm has been measured between 4.2 K and 300 K and a residual resistivity ratio of ~40 has been found. The experimental study of the I C (T,B) surface, of the thermal conduction properties κ(T,B), and of the matrix electrical resistivity ρ norm provides fundamental elements for a quench propagation study, which is critical in view of high-field applications of this conductor.

A topological semimetal PtSn4 single crystal was grown by method of crystallization from a solution in a melt. Then the electrical resistivity and galvanomagnetic properties (magnetoresistivity and the Hall effect) were studied in the temperature range from 4.2 to 80 K and in magnetic fields up to 100 kOe. The optical measurements were carried out at room temperature. The residual resistivity is shown to be low enough and amount to ∼ 0.5 μOhm•cm. The temperature dependence of the electrical resistivity has a metallic type, increasing monotonically with temperature. A sufficiently large magnetoresistance of 750% is observed. The majority carriers are supposed to be holes with a concentration of ∼ 6.8•10 21 cm -3 and mobility of ∼ 1950 cm 2 /Vs at T = 4.2 K as a result of the Hall effect studies. The optical properties of PtSn 4 have features characteristic of "bad" metals. © 2019 Published under licence by IOP Publishing Ltd. This work was partly supported by the state assignment of Russia (theme “Spin” No. АААА-А18-18020290104-2 and theme “Electron” No. АААА-А18-118020190098-5), by the RFBR (project No.17-52-52008) and by the Government of the Russian Federation (state contract No. 02.A03.21.0006).

We developed a soft and high thermal conductive thermal link for cryogenic applications. The measured maximum thermal conductivity was approximately 18500 W / m / K at 10 K. This spring constant was 1/43 of that of a single thick wire with the same cross-sectional area at room temperature. We reached these performances by utilizing high purity aluminum (99.9999 % , 6 N) and by stranding many thin wires that are 0.15 mm in diameter. The electrical Residual Resistivity Ratio was also measured and used to estimate the thermal conductivity by the Wiedemann–Franz law. We observed the size effect on the electrical conductivity, and evaluated the effect of mechanical deformation to the RRR. These evaluations allow us to design a pragmatic thermal link for cryogenic application.

We report the enhanced superconducting properties of double-chain based superconductor Pr 2 Ba 4 Cu 7 O 15 − δ synthesized by the citrate pyrolysis technique. The reduction heat treatment in vacuum results in the appearance of superconducting state with T c =22-24 K, accompanied by the higher residual resistivity ratios. The superconducting volume fractions are estimated from the ZFC data to be 50 ∼ 55 % , indicating the bulk superconductivity. We evaluate from the magneto-transport data the temperature dependence of the superconducting critical field, to establish the superconducting phase diagram. The upper critical magnetic field is estimated to be about 35 T at low temperatures from the resistive transition data using the Werthamer-Helfand-Hohenberg formula. The Hall coefficient R H of the 48-h-reduced superconducting sample is determined to be − 0.5 × 10 − 3 cm 3 /C at 30 K, suggesting higher electron concentration. These findings have a close relationship with homogeneous distributions of the superconducting grains and improved weak links between their superconducting grains in the present synthesis process.

Improvement of superconducting properties of MgB2 superconductor becomes necessary in several medium and large scale commercial practical applications where generation of high magnetic field is of significant interest. High power cables, energy storage devices, wind turbines and magnetic resonance imaging are the potential areas of application where MgB2 superconductor with improved property is indispensable. In order to facilitate quick determination of transition temperature of MgB2 superconductor and to determine the conditions at which this superconducting property is optimal for the desired application, this present contribution hybridizes genetic algorithm (HGA) with support vector regression (SVR) machine learning to model the transition temperature of doped MgB2 superconductor using ambient room temperature resistivity (RTR), residual resistivity ratio (RRR) and structural lattice distortion (SLD) due to the incorporated dopants as descriptors. The developed HGA-SVR-RTR model that utilizes RTR as descriptor shows better performance than the proposed HGA-SVR-RRR model (that employs RRR as descriptor) and HGA-SVR-SLD model (that implements SLD as descriptors) with improvement in performance by 88.45% and 71.41%, respectively using mean absolute error (MAE) as a parameter that evaluates the model performance. The developed HGA-SVR-RTR model also outperforms the existing models such as GPR-prediction (2020), STTE model (2016) and STTE model (2014) with performance improvement of 74.85%, 74.76% and 92.96%, respectively using MAE as a yardstick for performance comparison. The developed HGA-SVR-RRR model performs better than HGA-SVR-SLD model with percentage improvement of 59.6% on the basis of MAE. The performance of the developed models would definitely facilitate cost effective search for doped MgB2 superconductor for desired application without experimental stress.

We performed combined experimental and theoretical studies of the effect of Cr substitution for Fe on the structural, magnetic, transport, electronic, and mechanical properties of Fe 3 - x Cr x Ge ( 0 ⩽ x ⩽ 1 ) intermetallic alloys. Single phase microstructures are observed for x ⩽ 0.70 . Higher Cr concentrations x > 0.70 are multi-phased. A hexagonal D0 19 structure is found for all Cr concentrations, with the lattice parameters increasing systematically with an increasing Cr content. All the alloys in the series are found to be ferromagnets with large magnetization values of about 6 μ B / f . u . and high Curie temperature above room temperature. The low-temperature saturation magnetic moments agree fairly well with our theoretical results and also obey the Slater-Pauling rule. The density functional theory calculation reveals that Cr substitution energetically favours one of the Fe sites in Fe3Ge. The electrical resistivity measured over the temperature range from 5 K to 400 K shows metallic behavior, with a residual resistivity ratio that decreases with Cr content. Vicker’s hardness values are observed to increase with increasing Cr content to approximately 5 GPa.