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Optimal conditions for obtaining high quality epitaxial Nb thin films on the monocrystalline sapphire R-plane by pulsed laser deposition in ultrahigh vacuum have been determined. The ratio of room temperature resistance to the residual resistance (RRR) on the substrate temperature has the maximum at about 630 °C. The RRR dependence on the growth rate has the maximum at growth rates of 3–6 nm/min. In epitaxial Nb films, there is a simultaneous increase in the value of RRR and growth misorientation of Nb(001) relatively sapphire R-plane. At the maximum value of RRR, the shapes of Nb X-ray diffraction (XRD) peaks (002) and (011) are symmetrical and close to the Gaussian distribution; at lower RRR values, the shapes of XRD peaks become asymmetrical and cannot be approximated by a single Gaussian distribution, and their shape can be described by the sum of several Gaussian functions. For all obtained films, full width at half maximum (FWHM) of Nb (002) and Nb (011) peaks are 0.2o and 0.4о, respectively. FWHM of Nb (002) rocking curves is 0.4o. • Epitaxial Nb films on the sapphire R-plane with the highest RRR values were obtained. • The comparison of the obtained RRR values with the literature data was carried out. • RRR values correlate with the tilt of the growth plane of Nb film. • RRR values correlate with the shapes of Nb X-ray diffraction peaks (002) and (011). [ABSTRACT FROM AUTHOR]

In the process of minimizing stress in sputtered molybdenum (Mo) films for fabricating transition-edge sensor devices, we have investigated correlations between the stress and film deposition parameters. At a fixed sputtering power, the tensile stress of our film samples decreases toward both low and high ends of Ar pressure, suggestive of two physical mechanisms at work: an ‘atomic peening’ effect at low Ar pressure and the development of voids at high Ar pressure. We have also carried out correlative studies of the stress and electrical properties (including superconducting critical temperature and residual resistivity) of the film samples, and found that the results are complex. We have made extensive comparisons with the published results, and attempted to explain the discrepancies in terms of film deposition techniques, sample preparation and treatment, and dynamical ranges of measurements. It is fairly clear that the microscopic properties, including porosity and disorder, of Mo films may have significant impact on the correlations. [ABSTRACT FROM AUTHOR]

The residual resistivity, Hall effect, and magnetization of Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were considered at T = 4.2 K and in fields up to 100 kOe. It is shown that as the number of valence electrons z ranges from 26 to 32, significant changes in the residual resistivity ρ0, magnetization Ms, sign and magnitude of the normal R0 and anomalous RS Hall effect coefficients are observed during the transition from Co2TiSi to Co2NiSi. It is established that there is a clear correlation between the values ρ0, R0, RS and Ms, depending on the number z, which can be associated with the appearance of a half-metal ferromagnetic state and/or spin gapless semiconductor. As z changes, the anomalous Hall effect coefficient has a power-law dependence on the residual electrical resistivity with an exponent of k = 3.1, which diverges with existing theories but agrees well with the experimental data obtained earlier for similar half-metallic ferromagnetic Heusler alloys. [ABSTRACT FROM AUTHOR]

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 \rhores 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_{0} . E_c$ increases from 100 to 150 kV/m, as soil water content decreases from 5% to 2%. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the nature of field-tuned metamagnetic quantum criticality in the ruthenate Sr3Ru2O7 has presented a significant challenge within condensed matter physics. It is known from experiments that the entropy within the ordered phase forms a peak, and is unexpectedly higher than that outside, while the magnetoresistivity experiences steep jumps near the ordered phase. We find a challenging connection between Sr3Ru2O7 and heavy-fermion metals expressing universal physics that transcends microscopic details. Our construction of the phase diagram of Sr3Ru2O7 permits us to explain main features of the experimental one, and unambiguously implies an interpretation of its extraordinary low-temperature thermodynamic in terms of fermion condensation quantum phase transition leading to the formation of a flat band at the restricted range of magnetic fields B. We show that it is the flat band that generates both the entropy peak and the resistivity jumps at the QCPs. [Copyright &y& Elsevier]

Abstract: High-quality Nb (110) thin films with residual resistance ratios up to 60 and critical temperatures T c ≈9.27K have been prepared by conventional dc-magnetron sputtering on α-Al2O3 by careful selection of the sputtering conditions. This allowed for a systematic study of the influence of the growth rate on the structural quality and the superconducting properties of the films. The optimized growth conditions were revealed at the substrate temperature T s =850°C, Ar pressure P s =0.4Pa, and the growth rate g ≃0.5nm/s. The results of the films'' structural characterization by X-ray diffraction, reflection high-energy electron diffraction, and atomic force microscopy are presented. In terms of the electron mean free path l and the superconducting coherence length ξ, deduced from the magneto-resistivity data, the clean superconducting limit (l > ξ) is realized in the high-purity films. For comparison, in impure Nb films sputtered at room temperature while keeping the rest of the sputtering parameters unvaried, the opposite dirty limit (ξ ≳ l) ensues. The merits of these findings are discussed in the context of the demands of present-day fluxonics devices regarding the normal-state and flux-flow properties of superconducting films they are made of. [Copyright &y& Elsevier]

The residual resistivity for 156 dilute alloys of 19 hosts of different groups of the periodic table has been studied on the basis of the single parametric model potential formalism. Ashcroft's empty core model (EMC) potential is explored for the first time with five different local field correction functions, viz, Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F), and Sarkar et al. (S) to investigate the effect of the exchange and correlation on the aforesaid properties. The comparison of the presently computed outcomes with the available theoretical and experimental data is highly encouraging. The investigation of residual resistivity is found to be quite sensitive to the selection of local field correction function, showing a significant variation with the change in the function. [ABSTRACT FROM AUTHOR]

Abstract: Resistivity and low-field (40A/m) susceptibility measurements are performed on the samples of Y0.95Pr0.05Ba2(Cu1−x Mn x )3O7−δ (x ⩽0.02). It has been observed that above x =0.005 resistivity decreases drastically in the presence of Pr atoms. Analyzing this feature it has been argued that potential scattering alone is inadequate for explaining the resistivity behaviour. Prominent role of the electronic effects is expected for increasing Mn content. Analyzing the imaginary part of ac susceptibility at the peak temperatures it has been found that the superconducting volume fraction f g is 0.12 for x =0, but reduces drastically to 0.03 for x =0.005. For other values of x, f g is higher than 0.12. [Copyright &y& Elsevier]

Partial discharge of soil occurs when a lightning current enters the ground, and the strength of partial discharge is closely related to the magnitude of its critical breakdown field strength. Therefore, how to accurately obtain the variation law of the typical soil critical breakdown field strength and residual resistivity is the key to realizing the safe operation of the grounding devices and cables in the ground. This paper first selects a variety of typical soils to study the influence of various factors on the morphology of the discharge channel, and then studies the calculation methods of the soil critical breakdown field strength and residual resistivity under the introduction of different discharge channel morphologies and structures, and further discusses the reason why typical soil media factors have a small impact on the critical breakdown field. The experimental results show that under the same conditions, the critical breakdown field strengths of different soils from small to large are sand soil, loam soil and Yellow cinnamon soil. The largest ratio of residual resistivity to initial resistivity of the three soils is sand soil. [ABSTRACT FROM AUTHOR]

The residual resistivity of copper stabilizer (/spl rho/), is deteriorated by the diffusion of chromium plated on the strand surface during heating of Nb/sub 3/Al strands. To improve this degradation, the copper stabilizer has been located on the center of the cross-section of the strand rather than near the strand surface. As a result, /spl rho/ is improved to one-sixth of previous value achieving 1.6/spl times/10/sup -10/ /spl Omega/m in a laboratory scale strand. The critical current density (J/sub c/) of this strand was 715 A/mm/sup 2/ at 12 T. This technique was applied to prototype strands to be used in a Nb/sub 3/Al Insert Coil developed in ITER R&D programme resulting in a /spl rho/ of 1.5/spl times/10/sup -10/ /spl Omega/m, which meets ITER specification. In addition, the improvement of J/sub c/ was also studied by two-stage reaction including a continuous heating procedure, which resulted in a J/sub c/ of 1130 A/mm/sup 2/ at 12 T and good longitudinal uniformity. [ABSTRACT FROM PUBLISHER]

Abstract: In this communication we present some theoretical results of specific heat and thermoelectric power of the superconductor GdBa2(Cu1− x Mn x )3O7−δ (for x ⩽0.02). A model based on separate electronic and phononic contributions is used for the interpretation of the specific heat data while a narrow band model is used for the analysis of thermoelectric power. On the basis of these models two main conclusions have been drawn about the relative effects of different Mn contents: (1) the observed fluctuation effects near Tc whose strength increases with increasing Mn content and (2) Mn produces mainly electronic effects for lower Mn contents, while for higher doping levels (x >0.0075) Mn predominantly causes carrier-Mn scattering process. [Copyright &y& Elsevier]

• Soil ionization does not produce infinite electrical conductivity or zero resistivity. • Ionization of water solutions and gases are closely related to multi-stage wet ground ionization. • Finite-difference time-domain (FDTD) method can be used to precisely model soil multi-stage ionization along with geometrically complex grounding electrodes. In this first part of the paper, a Finite-Difference Time-Domain (FDTD) model for multi-stage soil ionization with residual resistivities is proposed to obtain realistic transient responses of grounding systems subjected to high intensity currents. Four phases of soil ionization process are modeled: non-ionization (linear soil representation), presparking (first stage of ionization), sparking (second stage of ionization) and deionization. Mechanisms identified experimentally in literature for water ionization explain presparking and sparking phases of soil ionization. Weak ionization in clusters of gas bubbles produced due to high current flows explains the presparking phase. The sparking phase is governed by ionization of aqueous solutions in soil. A mathematical function is defined to represent the rise of electrical conductivity over time for each point in the soil FDTD lattice during sparking phase. Additionally, effects associated with limited production of free charges over time and their increasing reduction of mobility are considered by means of residual resistivities in presparking and sparking phases. Due to the complex nature of the phenomenon, which involves various physical processes, comprehensive theoretical background is also provided in part I. The second part of the paper presents numerical validation cases for the proposed FDTD soil ionization model. [ABSTRACT FROM AUTHOR]

Abstract: We discuss the temperature-independent resistivity of nd transition metal impurities diluted in Cu host, using a T-matrix formulation in a single band system. We take into account the translational symmetry breaking introduced by the impurity and therefore a non-local charge potential is obtained. The effect of volume difference between impurity and host elements is also considered in the calculation. Our numerical results describe quite well the available experimental data. [Copyright &y& Elsevier]