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The Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) has announced a project to design and manufacture a high field MRI magnet with a 900 mm warm bore and comprised of Nb3Sn Rutherford cables in 2017. The maximum magnetic induction of magnet system is 14.3 T and magnetic field homogeneity in a spherical volume with 22 cm diameter is better than 0.5 ppm. The high performance Nb3Sn strand is the potential options to use for such high field magnet system. ASIPP cooperates with Western Superconducting Technologies Company (WST) to develop high performance Nb3Sn strand whose critical current density Jc is higher than 2000 A/mm2 at 4.2 K, 12 T. To obtain the actual performance of WST high performance Nb3Sn strand, three short samples are prepared with different non-copper ratio or different heat treatment, the critical current Ic or quench current of all sample is measured at different field by the voltage-current (V-I) method, the residual resistivity ratio (RRR) of all sample is also measured. To study the strand whether it will be affected by low field instability, a small coil is built with WST strand, and the experimental result is presented and discussed in this paper.

The introduction of carbon interstitials into high-entropy alloys (HEAs) provides an effective way to improve their properties. However, all such HEA systems explored so far are limited to those with the face-centered-cubic (fcc) structure. Here we report the structural, mechanical and physical properties of the refractory (Nb0.375Ta0.25Mo0.125W0.125Re0.125)100−xCx HEAs over a wide x range of 0 ≤ x ≤ 20. It is found that, whereas the starting HEA (x = 0) is composed of a major body-centered-cubic (bcc) phase with significant impurities, the bcc phase fraction increases with the C concentration and achieves almost 100% at x = 20. Moreover, the increase of C content x results in an expansion of the bcc lattice, an enhancement of the microhardness, an increase in residual resistivity and a small variation of density of states at the Fermi level. All these features are consistent with the expectation that carbon atoms occupy the interstitial site. For x ≥ 11.1, the X-ray photoelectron spectroscopy indicates the bond formation between the carbon and metal atoms, suggesting that some carbon atoms may also reside in the lattice site. In addition, a semiquantitative analysis shows that the enhanced mixing entropy caused by carbon addition plays a key role in stabilizing the (nearly) single solid-solution phase. Our study not only provides the first series of carbon interstitial HEAs with a bcc structure, but also helps to better understand the alloying behavior of carbon in refractory HEAs.

Epitaxial strain in 4d ferromagnet SrRuO3 films is directly linked to the physical properties through the strong coupling between lattices, electrons, and spins. It provides an excellent opportunity to tune the functionalities of SrRuO3 in electronic and spintronic devices. However, a thorough understanding of the epitaxial strain effect in SrRuO3 has remained elusive due to the lack of systematic studies. This study demonstrates wide-range epitaxial strain control of electrical and magnetic properties in high-quality SrRuO3 films. The epitaxial strain was imposed by cubic or pseudocubic perovskite substrates having a lattice mismatch of -1.6 to 2.3% with reference to bulk SrRuO3. The Poisson ratio, which describes the two orthogonal distortions due to the substrate clamping effect, is estimated to be 0.33. The Curie temperature (TC) and residual resistivity ratios of the series of films are higher than or comparable to the highest reported values for SrRuO3 on each substrate, confirming the high crystalline quality of the films. A TC of 169 K is achieved in a tensile-strained SrRuO3 film on the DyScO3 (110) substrate, which is the highest value ever reported for SrRuO3. The TC (146-169 K), magnetic anisotropy (perpendicular or in-plane magnetic easy axis), and metallic conduction (residual resistivity at 2 K of 2.10 - 373 {\mu}{\Omega}cm) of SrRuO3 are widely controlled by epitaxial strain. These results provide guidelines to design SrRuO3-based heterostructures for device applications.

LCNMO (La0.7Ca0.26Na0.04MnO3) ceramics are prepared via the sol-gel method and sintered at different temperatures, ranging from 1000 to 1300 °C. The influences of sintering temperature on structure and electrical properties are systematically investigated. X-ray diffraction analysis reveals that uniform phase of perovskite structure is formed after sintering. Furthermore, scanning electron microscope (SEM) images demonstrate the presence of on the surface, a highly dense grain boundary and an average grain size of ~2.5 μm. The resistivity-temperature (ρ-T) measurement shows that the resistivity decreases with increased sinter temperature. Moreover, the metal-insulation transition temperature (Tp) and peak resistivity (ρmax) gradually decreased with increasing sintering temperature. The influence of various scattering mechanisms on resistivity at low temperatures is studied, revealing that the residual resistivity (ρ0) dictates the electrical transport performance of the LCNMO ceramics. Also, the different models employed to analyze the ρ-T curves in the temperature range of 100–300 K, confirming the occurrence of phase-separation mechanism in the entire temperature range. The resistance temperature coefficient (TCR) of 10.6%·K−1 and maximum magnetic resistance (MRmax) of 57.12% are achieved after sintering at 1200 °C. These results indicate that LCNMO are promising candidates for infrared detector and magnetic sensor.

In this work, a series of FeS1-xTex (0 ≤ x ≤ 0.15) single crystals were successfully synthesized by a hydrothermal method for the first time. According to the measurement of in-plane resistivity, Hall effect, and magnetoresistance (MR), we find that the superconducting transition temperature Tc is rapidly suppressed with the increasing Te substitution, and finally the superconductivity disappears when x > 0.05. With the substitution of Te for S, the residual resistivity ρ0 increases while the residual resistivity ratio (RRR) decreases monotonously. Meanwhile, the MR of FeS1-xTex is also reduced by Te doping. All these results reveal that the Te substitution introduces more impurity scattering. In consequence, the non-linear field-dependent of Hall resistivity ρxy at low temperature region is suppressed and a linear behavior is restored upon Te doping. The negative Hall coefficients RH for all the FeS1-xTex samples suggest that the electron-type carrier dominates the electrical conduction. Moreover, the MR of FeS1-xTex obviously follows Kohler’s law, indicating the isotropic scattering rates in the Fermi surface.

This article focuses on the effect of grain size on estimating the residual resistivity ratio (RRR) of electron beam welded (EBW) high purity Niobium (Nb) for the structural fabrication of radio frequency cavity as a particle accelerator. This also aims to investigate the effects of using different functional models on resistivity. EBW is done by varying the beam current to change the grain size so that its consequent impact on RRR can be evaluated. Grain size was found to be maximum for 70 mA and minimum for 50 mA beam current among the welded samples at HAZ and FZ. The grain size increases from the base metal toward the heat-affected zone and further to the fusion zone like any other fusion welding processes. Pure Nb being electrically superconductive below around 9.2 K in the absence of any magnetic field, it is invariably used as a resonant cavity for a particle accelerator in high energy physics. Two temperature dependent and two field dependent models are used for extrapolation of the RRR value estimation. Temperature dependent models performed the better-fitted residuals for every sample than the field models. The extrapolated RRR values obtained from these models are used to simulate the impact of beam current on grain size at different zones of welding.

CeSb2 is a homologue of rare-earth diantimonides. This work reports a systematic study of a series of high-quality single crystals of CeSb2 grown by a self-flux method, which is a heavy fermion Kondo metal with intricate magnetic transitions. We have grown four types of crystals with different initial material ratios in order to investigate the effect of growth conditions on the quality of the as-grown crystals. The phase purity, morphology and composition of the synthesized samples were studied with X-ray diffraction, scanning electron microscopy, electron-probe microanalysis, and Raman-scattering spectroscopy to evaluate their quality. It is found that an inappropriate raw material ratio will lead to the inhomogeneity and poor crystallinity of the as-grown crystal. In addition, the electrical transport properties of the as-grown crystals were measured, from which the residual resistivity ratios were extracted to further examine the homogeneity and crystalline quality. Furthermore, the magnetoresistance properties of CeSb2 were observed. Through a systematic study on CeSb2, the most suitable starting ratio for the growth of CeSb2 was obtained, which might serve as a guide for the growth of other light rare-earth diantimonides.

Distortion of the density of states induced by specific impurities, a mechanism known as resonant level (RL), is an efficient strategy to enhance the thermoelectric performances of metals and semiconductors. So far, experimental signatures identifying the resonant nature of an impurity have relied on the so-called Ioffe–Pisarenko plot that enables visualizing the induced thermopower enhancement at specific carrier concentrations. However, this method cannot solely discern RL from other possible band-structure-related sources of thermopower enhancement such as band-shape modifications or band convergence. An independent method of resolving this problem is proposed here. A detailed theoretical and experimental analysis of the low-temperature electrical resistivity ρ0 and carrier mobility μ0 of the resonant-level system SnTe doped with In is presented as a function of the impurity concentration x. By comparing to non-resonant cases of SnTe doped with I, Mn, and Ga, we demonstrate that the construction of residual resistivity ρ0(x) and residual mobility μ0(x) plots allows to distinguish between resonant and non-resonant impurities, even when some of them induce similar thermopower enhancements. This methodology is further confirmed by analyses performed for Na- and Tl-doped PbTe, illustrating how the combination of transport measurements at low temperatures can be used to determine the resonant nature of an impurity.

Undoped, Eu- and La-doped CuS nanoparticles stabilized by l-cysteine were synthesized by a low-temperature soft aqueous route. Their structural properties were investigated by X-ray powder diffraction, their morphological properties were scrutinized using scanning electron microscopy, their microstructural properties were carried out using transmission electron microscopy, their optical properties were examined using ultraviolet–visible spectroscopy, and their electrical properties were studied using complex impedance spectroscopy. It was found that Cu0.99La0.01S nanoparticles exhibit the smallest particle size, the highest optical bandgap, the highest values of electrical conductivity and dielectric constant, and the lowest values of dielectric loss tangent when compared with CuS and Cu0.99Eu0.01S nanoparticles. To investigate the effect of the as-synthesized nanoparticles on the superconducting properties of bismuth-based compound ((Bi,Pb)2Sr2Ca2Cu3Oδ), its structural properties were examined by X-ray powder diffraction, its transport properties were analyzed by the standard four-probe technique, its intrinsic properties were investigated using the Aslamazov–Larkin approach and its pinning properties were studied using the thermally activated flux flow model. It was found that Cu0.99La0.01S added sample exhibits the highest Bi-2223 phase concentration, the lowest residual resistivity, the highest critical transition temperature, the lowest value of coherence length, the highest values of penetration depth, upper critical magnetic field and critical current density, the narrowest shift of the zero-resistivity temperature, the highest effective pinning energies and the highest global critical current densities, when compared with pure, CuS and Cu0.99Eu0.01S added samples.

For developing a 14 Tesla whole-body superconducting magnetic resonance imaging (MRI) magnet, a new kind of a Nb3Sn composite conductor with Rutherford cable-in-channel (RIC) structure is adopted. This structure of the conductor has a high current carrying capacity with an increased thermal and mechanical stability. The Rutherford cable is the core component of the RIC conductor, and controlling the deformation and performance degradation of Nb3Sn strand are the key points in Rutherford cable development. The strand would experience plastic deformation during the compaction process, which causes sub-elements damage and degrades the transport performance and residual resistivity ratio (RRR). In this paper, the impact of transverse compression on the sub-element of RRP 84/91 Nb3Sn strand before heat treatment was studied with experiments and finite element model (FEM), the experiment results and FEM results were compared and analyzed. Experiment results show that the transverse deformation of the strand should be kept below 20% to avoid the Nb barrier from breaking. The deformation analysis result of the FEM simulation shows good agreement with experimental results.

A project aiming to fabricate a full-length 2.8-m long Nb3Sn superconducting undulator for the storage ring was started last year at the ANL APS. These Nb3Sn undulators operate at a maximum magnetic field on the conductor of about 5 T. To address instabilities at this field, two Nb3Sn wires with small subelement size were used. Specifically, Restacked Rod Processed wires of 0.6 mm in diameter and with 144 and 150 superconducting subelements respectively, over 169 total. The equivalent subelement diameter, DS , of these wires is ∼35 μm. At these small DS values, the critical current density is known to deteriorate, and the Residual Resistivity Ratio is very sensitive to heat treatment. A delicate balance has therefore to be found to obtain parameters within operation specifications. In this paper we show performance results from different heat treatments.

We describe the effect of nonmagnetic impurity on the superconductivity behavior of the NdFeAsO0.8F0.2 iron-based superconductor. The resistivity measurements show that the superconductivity is suppressed upon increasing the low amounts of calcium impurity (x ≤ 0.05). Also, the TC decreases with the increase in the residual resistivity. Such behavior is qualitatively described by the Abrikosov–Gorkov theory and confirms that these impurities act as scattering centers. Moreover, we present the phase diagram of our synthesized samples for the various calcium dopings. We find that according to the increase in the calcium impurities and the decrease in the spin-density wave transition tempeθrature (TSDW), Fe ions are arranged stripe-antiferromagnetic at lower temperatures and also the superconducting transition temperature (TC) declines. Based on our results and in agreement with the available theories as is explained in the text, since the S++ state has no effect on the impurity-doped samples, and for low amounts of calcium, the S± state that is attributed to the spin-fluctuations causes the superconductivity suppression. So, it confirms the role of the spin-fluctuations as a dominant pairing mechanism in our synthesized samples.

The changing thermal conductivity of an irradiated material is among the principal design considerations for any nuclear reactor, but at present few models are capable of predicting these changes starting from an arbitrary atomistic model. Here we present a simple model for computing the thermal diffusivity of tungsten, based on the conductivity of the perfect crystal and resistivity per Frenkel pair, and dividing a simulation into perfect and athermal regions statistically. This is applied to highly irradiated microstructures simulated with molecular dynamics. A comparison to experiments shows that simulations closely track observed thermal diffusivity over a range of doses from the dilute limit of a few Frenkel pairs to the high-dose saturation limit at three displacements per atom (dpa).

Superconductivity induced by a magnetic field near metamagnetism is a striking manifestation of magnetically-mediated superconducting pairing. After being observed in itinerant ferromagnets, this phenomenon was recently reported in the orthorhombic paramagnet UTe$_2$. Under a magnetic field applied along the hard magnetization axis b, superconductivity is reinforced on approaching metamagnetism at $\mu_0H_m$ = 35 T, but it abruptly disappears beyond $H_m$. On the contrary, field-induced superconductivity was reported beyond $\mu_0H_m$ = 40-50 T in a magnetic field tilted by $\simeq25-30\deg$ from b in the (b,c) plane. Here we explore the phase diagram of UTe2 under these two magnetic-field directions. Zero-resistance measurements permit to confirm unambiguously that superconductivity is established beyond Hm in the tilted-field direction. While superconductivity is locked exactly at fields either smaller (for a H || b), or larger (for H tilted by $\simeq27\deg$ from b to c), than Hm, the variations of the Fermi-liquid coefficient in the electrical resistivity and of the residual resistivity are surprisingly similar for the two field directions. The resemblance of the normal states for the two field directions puts constraints for theoretical models of superconductivity and implies that some subtle ingredients must be in play., Comment: 18 pages, 5 Figures, includes Supplementary Information (9 pages, 8 Figures)

International audience; The family of Co-based Heusler compounds contains promising candidates for spintronic applications regarding their predicted Half-Metal-Magnetic nature, ultra-low magnetic damping coefficients, high curie temperatures and tunable electronic properties. Here we focused on the transport properties of Co2MnSi thin films with thickness in the range of 4-44 nm exhibiting magnetic damping in the 10-4 range. The goals of this study are to examine the impact of the peculiar electronic band structure on the transport properties, to identify the temperature-dependent scattering process, and to extract robust conduction parameters to exploit this material in magnetoelectric devices. In order to undoubtedly correlate all results, the full study has been performed on the same series of samples. Scanning transmission electron microscopy experiments were performed to check the chemically-ordered L21 phase in our films, and also allowed us to identify misfit dislocations generated at the interface with the substrate. The variation of the resistivity with film thickness was measured at different temperatures. The results are examined under the Fuchs and Sondheimer model which allowed us to extract the electron mean free path in Co2MnSi in the temperature range 5-300 K. Values for the residual resistivity, Debye temperature, and distance between the Fermi energy and the conduction band for minority spins were obtained from the fit of the resistivity versus temperatures curves. A negative AMR ratio was measured for all the samples which confirmed the Half-metallic nature of the Co2MnSi films. The determination of the ordinary Hall coefficient alloys allowed us to extract the carrier concentration and carrier mobility and their dependency on the temperature. Finally, scaling of the anomalous Hall coefficient with the longitudinal resistivity was performed indicating that skew scattering is the dominant temperature-dependent scattering mechanism in our films.

We revisit a superconducting phase diagram and electronic structures across the charge density wave (CDW) phase transition of Cu-underdoped $1T\text{\ensuremath{-}}{\mathrm{Cu}}_{\ensuremath{\delta}}\mathrm{Ti}{\mathrm{Se}}_{2}$ ($\ensuremath{\delta}\ensuremath{\sim}0.03$) under hydrostatic pressure. Superconductivity appears right after the complete collapse of the long-range CDW at a critical pressure of ${P}_{\mathrm{c}}\ensuremath{\sim}2.48\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, apart from the reported superconducting phase diagrams; it is found that the superconducting transition temperature shows a domelike pressure dependence covering a narrow pressure range with a maximum of ${{T}_{\mathrm{c}}}^{\mathrm{max}}\ensuremath{\sim}2.80\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 4.80 GPa. Accordingly, the residual resistivity ${\ensuremath{\rho}}_{0}$ and temperature exponent $n$ of normal-state resistivity (from \ensuremath{\sim}3.30 at ambient pressure to \ensuremath{\sim}2.38 at ${P}_{\mathrm{c}}$ and \ensuremath{\sim}4.0 at 6.50 GPa) reduce sizably while the quadratic temperature coefficient $A$ of normal-state resistivity is enhanced by one order in magnitude; these results indicate the importance of CDW quantum fluctuation in superconducting pairing; low-$T$ resistivity upwarps with a \ensuremath{-}ln$T$ dependence below a characteristic temperature ${T}^{*}$ which has a domelike shape in the pressure range of 2.82--4.80 GPa. Based on two-band analysis of Hall conductivity and Kohler-fitting of magnetotransport (MR), energy bands are dominated by electron-type carriers across the CDW phase transition for $Pl{P}_{\mathrm{c}}$, and they reverse into hole-type for $Pg{P}_{\mathrm{c}}$; interestingly, the mobility of carriers increases up to five times at ${P}_{\mathrm{c}}$, but carrier concentration shows a weak pressure dependence. The MR value increases with the pressure for $Pl{P}_{\mathrm{c}}$ and then jump up to a saturated value after the collapse of the CDW. Our results show that the collapse of the CDW is accompanied by the reconstruction of the Fermi surface, and the enhancement in MR can be mainly attributed to the change of mobility. Possible mechanisms are discussed.

The Kubo-Greenwood equation, in combination with the first-principles Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) can be used to calculate the DC residual resistivity of random alloys at T = 0 K. We implemented this method in a multiple scattering theory based ab initio package, MuST, and applied it to the ab initio study of the residual resistivity of the high entropy alloy Al$_x$CoCrFeNi as a function of $x$. The calculated resistivities are compared with experimental data. We also predict the residual resistivity of refractory high entropy alloy MoNbTaV$_x$W. The calculated resistivity trends are also explained using theoretical arguments., 18 pages, 9 figures (not including Supplementary Material). The article has been submitted to Applied Physics Letters

This paper reports a comprehensive study of electrical and thermal transport properties of a series of face-centered cubic structured high-entropy alloys by alloying Mn, Cr, and Pd elements in NiCo, NiFe, and NiCoFe alloys. X-ray diffraction revealed a single-phase Cu-type cubic structure, and scanning electron microscopy displayed elongated grained microstructures in all alloys. Like NiCo, NiFe, and NiCoFe alloys, the alloys containing Cr/Mn/Pd exhibit metallic behavior; however, their electrical transport properties, such as residual resistivity, residual resistivity ratio, and temperature coefficient of resistivity, vary significantly due to the increase of chemical disorder and defects. The analysis of resistivity of these alloys further showed different scattering mechanisms at low temperatures. Interestingly, the electrical resistivity of NiCoCr, NiCoFeCr, and NiCoFeMn alloys is nearly linear at low temperatures, most likely related to the Mott-Ioffe-Regel limit. Additionally, the NiCoMnCr and NiCoFeMnCr alloys exhibit a minimum in resistivity at low temperatures, which can be explained by the weak localization effect. The Seebeck coefficient measurements reveal that the charge carrier for thermoelectric transport in NiCo, NiFe, and NiCoFe is changed from electrons to holes with Mn alloying. In contrast, a sign reversal of the charge carriers observed in the Cr-containing alloys is connected to the compensation of electron and hole carriers. Furthermore, the NiCoCr, NiCoFeCr, NiCoMnCr, and NiCoFeMnCr alloys show a negative phonon drag effect at low temperatures due to electron-phonon interaction. The measured thermal conductivity behaves similarly in all alloys, except for a considerable reduction in magnitude in Cr/Mn/Pd-containing alloys. This is attributed to a significant decrease of electronic thermal conductivity due to an increased electron scattering by disorders and lattice distortions and a substantial modification of band structure. There is almost an equal contribution of electronic and lattice to the total thermal conductivity in Cr/Mn/Pd-containing alloys, suggesting a semimetallic nature. The temperature dependence of lattice thermal conductivity of these alloys is described by different phonon scattering mechanisms.

Advances in physical vapor deposition techniques have led to a myriad of quantum materials and technological breakthroughs, affecting all areas of nanoscience and nanotechnology which rely on the innovation in synthesis. Despite this, one area that remains challenging is the synthesis of atomically precise complex metal oxide thin films and heterostructures containing “stubborn” elements that are not only nontrivial to evaporate/sublimate but also hard to oxidize. Here, we report a simple yet atomically controlled synthesis approach that bridges this gap. Using platinum and ruthenium as examples, we show that both the low vapor pressure and the difficulty in oxidizing a “stubborn” element can be addressed by using a solid metal-organic compound with significantly higher vapor pressure and with the added benefits of being in a preoxidized state along with excellent thermal and air stability. We demonstrate the synthesis of high-quality single crystalline, epitaxial Pt, and RuO(2) films, resulting in a record high residual resistivity ratio (=27) in Pt films and low residual resistivity, ∼6 μΩ·cm, in RuO(2) films. We further demonstrate, using SrRuO(3) as an example, the viability of this approach for more complex materials with the same ease and control that has been largely responsible for the success of the molecular beam epitaxy of III-V semiconductors. Our approach is a major step forward in the synthesis science of “stubborn” materials, which have been of significant interest to the materials science and the condensed matter physics community.

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.

The transition metal dichalcogenide $\mathrm{Ti}{\mathrm{Se}}_{2}$ is an ideal correlated system for studying the interplay between superconductivity (SC) and a charge density wave (CDW) because both symmetry-breaking phases can be easily controlled by either Cu intercalation or physical pressure. SC appears in proximity to a CDW quantum critical point (QCP) induced by both Cu intercalation and applied pressure, raising the possibility of CDW-driven SC. Here, we report tuning the CDW QCP by simultaneously controlling Cu intercalation and external pressure and the appearance of a SC dome centered on the tunable QCP. When subjected to pressure, CDW ordering of Cu-intercalated ${\mathrm{Cu}}_{0.025}\mathrm{Ti}{\mathrm{Se}}_{2}$ is completely suppressed at 2.3 GPa, where the residual resistivity and the resistivity-temperature exponent decrease sharply, indicating the presence of the CDW QCP. The upper critical field of ${\mathrm{Cu}}_{0.025}\mathrm{Ti}{\mathrm{Se}}_{2}$ is 3.51 kOe, 16 times larger than that of pristine $\mathrm{Ti}{\mathrm{Se}}_{2}$, and its temperature dependence is linear, indicating that SC of $\mathrm{Ti}{\mathrm{Se}}_{2}$ is switched from the two-dimensional- to anisotropic three-dimensional-like by Cu intercalation. These discoveries show that the simultaneous application of Cu intercalation and pressure move the CDW QCP and that the highest SC transition temperature is pinned to the QCP, suggesting that the SC in $\mathrm{Ti}{\mathrm{Se}}_{2}$ is strongly correlated with CDW quantum criticality.

Detailed analysis reveals that an incorporation of stabilized defect complexes within metallic thin films, though a highly disordering and nonequilibrium process, gives rise to superconductivity, Fermi-liquid (FL) transport, and a universal correlation among them. This remarkable manifestation of correlated macroscopic quantum effects is attributed to a phonon-mediated electron-electron, e-e, scattering channel which encompasses both Koshino-Taylor and Bergmann's pseudo-Umklapp processes. This channel---denoted below as pseudo-Umklapp e-e scattering channel---is distinctly different from traditional ones in that disorder leads to a breakdown of lattice momentum conservation (significantly enlarging available phase space), to a spectral weight transfer towards lower frequencies (modifying electron-phonon coupling constant $\ensuremath{\lambda}$), and to a relaxation of kinematic constraints (all phonic polarization modes become available for mediation). On modeling the distorted structure in terms of Hosemann's paracrystal and using standard quantum many-body techniques, we demonstrate the role of distortion and softening in establishing this pseudo-Umklapp channel and, consequently, the surge of superconductivity, the FL transport, and the correlation of their parameters. This unifying approach allows us to derive analytical expressions for ${T}_{c}({\ensuremath{\rho}}_{\ensuremath{\circ}})$ (hallmark of superconductivity), the coefficient $A({\ensuremath{\rho}}_{\ensuremath{\circ}})$ (hallmark of FL transport), and the universal kinematic scaling relation $\mathrm{ln}(\frac{{T}_{c}}{\ensuremath{\theta}})\ensuremath{\propto}{A}^{\frac{\ensuremath{-}1}{2}}$: All are in satisfactory agreement with experiments ($\ensuremath{\theta}$ is an energy scale; residual resistivity ${\ensuremath{\rho}}_{\ensuremath{\circ}}$ measures the extent of disorder).

We studied the effect of growth parameters on the phase formation of Fe4N in a reactive sputtering process. The Fe4N phase formation was found to be extremely sensitive to N2 gas flow and sputter rate but not so much on the substrate temperature. But post-deposition annealing (PDA) time was found to be a critical parameter to get single phase Fe4N. As PDA time increases, the anti-bonding states characteristic of Fe4N start to diminish due to N out-diffusion. Signatures of such N diffusion process can also be seen from the Fe and N depth profiles. We found that the residual resistivity ratio was maximum for the optimized Fe4N films. Magnetization measurements were performed using bulk magnetization as well as polarized neutron reflectivity. We found that the magnetic moment of optimized Fe4N film was about 2.3 μB/atom at 15 K. Magnetic anisotropy measurements carried out using magneto optical-Kerr effect exhibit a rotatable anisotropy.

The Residual Resistivity Ratio (RRR) is an important parameter which is used to determine the purity and thermal conductivity of Niobium (Nb) utilized for fabrication of Superconducting Radio Frequency (SRF) cavities. The usual 4-probe electrical resistance measurement method is both destructive in nature and produces a non-local (average) measurement of the electrical conductivity. The present work utilizes Printed Circuit Board (PCB) based planar inductor as sensing element. The impedance variation of the sensing element in the presence of a conducting metal (Nb), is used to determine the conductivity of the Nb target. A generalized equation for RRR is proposed in terms of parameters ‘a’ and ‘b’ associated with the sensing coil. The measurement method is experimentally verified by utilizing samples of Nb of known RRR values. The sensor parameters (‘a’ and ‘b’) are also established for cryogenic conditions. Errors in measurement, accuracy and repeatability of measurements down to 4.2 K are reported.

In this study, we determined the direct current DC isothermal magnetization (M − H and M-T), global critical current density (Jc), intra-grain critical current density (Jcintra), and excess conductivity for samples of CoFe2O4 (CFO; 1.0, 2.0, and 3.0 wt%) combined with Y1Ba2Cu3O7-δ (YBCO). X-ray diffraction analysis and Rietveld refinement suggested that all of the composite samples belonged to the Pmmm space group. No significant variations in the lattice parameters were observed after the inclusion of CFO in the YBCO matrix. The crystallite size decreased after CFO was added to the YBCO matrix according to field emission scanning electron microscopy. The addition of CFO to the YBCO matrix changed the flux pinning ability, thereby reducing the global critical current densities (Jc) and intra-grain critical current density (Jcintra) as the CFO concentration increased, but Jc and Jcintra both increased at the higher concentration., Jc and Jcintra were obtained from DC isothermal magnetization measurements (M − H) using Bean's critical state model. The critical temperature (TC) decreased and the residual resistivity (ρ0) increased as the wt.% of CFO increased, thereby indicating that the trapping of charge carriers occurred as well as grain boundary resistivity enhancement. Excess conductivity analysis was performed to investigate the thermal fluctuations near the critical temperature and various crossover temperatures were obtained using the Aslamazov–Larkin model.

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.

The variations of superconducting and mechanical properties of La0.67Sr0.33MnO3 (LSMO) [x = 0.0, 0.1, and 0.2] doped YBa2Cu3O7−δ (YBCO) composite thick films were examined. All the composite films were synthesized by diffusion reaction technique. The structural and morphological analysis were investigated through X-ray powder diffraction along with Rietveld refinement and Field emission scanning electron microscopy (FESEM) respectively. The transport measurement suggested that the inclusion of ferromagnetic LSMO decreases the superconducting transition temperature ( $$ T_{C}^{on} $$ ) and enhances the residual resistivity (ρ0). The broadening of resistive transition occurs below the onset transition temperature and shows the dissipative flux pinning. Various superconducting parameters were obtained from the excess conductivity analysis of the composite films and were in good agreement with the experimental findings. The mechanical strength of all the composite films was explained through different models like Hays–Kendall model, Elastic/Plastic deformation model and Proportional specimen resistance model.

A topological semimetal PtSn4 single crystal is grown and the following properties are studied: its electrical resistivity in the temperature range from 4.2 to 300 K, galvanomagnetic properties at temperatures from 4.2 to 80 K and in magnetic fields of up to 100 kOe, and optical properties at room temperature. Theoretical calculations of the electronic structure are performed. It is shown that the residual resistivity is rather small: ρ0 = 0.47 μΩ cm, which is characteristic of a “good” metal. The ρ(T) dependence is of the metallic type, increasing monotonically with temperature. Analysis of the temperature dependences of the magnetoresistivity suggests that the Fermi surface of the PtSn4 compound may contain closed sheets. Studies of the Hall effect and the estimates made in the single-band model allowed us to conclude that the predominant type of current carriers are holes with concentration n = 6.8 × 1021 cm–3 and mobility μ ≈ 1950 cm2/(V s) at T = 4.2 K. It is shown that the optical properties of PtSn4 have features characteristic of “bad” metals. The calculation of the electronic structure of PtSn4 showed that, in general, this compound has a structure characteristic of metallic systems with a sufficiently large number of electronic states at the Fermi level, which is consistent with the experimental results on the electronic transport and optical properties of the PtSn4 single crystal.

In this paper, the results of the superconductivity evaluation of MgB2 intermetallic-based superconducting materials prepared through mechanical alloying are reported. The formation of the MgB2 intermetallic phase took place through an intermediate phase reaction at the solid-state reaction temperature, which tends to favor single-phase materials. The annealing of mechanically milled Mg and B powders resulted in the highest mass fraction of MgB2 observed in this study, reaching more than 90% after annealing at 900 °C for 1 h. At that point, there were still second phases present consisting of Mg, MgO, and Fe2B. Improved superconducting properties were obtained in samples sintered at temperatures of 850 °C and 900 °C that had a low resistivity, low critical temperature gap values, and a high residual resistivity ratio (RRR).

The structural, magnetic and electron-transport properties of Fe2Ti0.5Co0.5Si are investigated. It is demonstrated that rapidly quenched Fe2Ti0.5Co0.5Si ribbons crystallize in the L21 structure, indicating a full Heusler compound, and exhibit ferromagnetism with a high Curie temperature of about 790 K. Moreover, Fe2Ti0.5Co0.5Si exhibits semiconducting behavior with a negative temperature coefficient of resistivity, a room-temperature resistivity of about 6.5 mΩ cm and a residual resistivity ρ0 of about 6.75 mΩ cm. The carrier concentration n is 1.15 × 1020 cm−3 at 5 K. The magnetic semiconducting behavior with a high Curie temperature makes this material promising for room-temperature spintronic and magnetic applications.

A study of Ti3Al1−xSixC2 (x = 0 to x = 1) MAX-phase alloys is reported. The materials were obtained from mixtures of Ti3AlC2 and Ti3SiC2 powders with hot pressing sintering technique. They were characterised with X-ray diffraction, heat capacity, electrical resistivity, and magnetoresistance measurements. The results show a good quality crystal structure and metallic properties with high residual resistivity. The resistivity weakly varies with Si doping and shows a small, positive magnetoresistance effect. The magnetoresistance exhibits a quadratic dependence on the magnetic field, which indicates a dominant contribution from open electronic orbits. The Debye temperatures and Sommerfeld coefficient values derived from specific heat data show slight variations with Si content, with decreasing tendency for the former and an increase for the latter. Experimental results were supported by band structure calculations whose results are consistent with the experiment concerning specific heat, resistivity, and magnetoresistance measurements. In particular, they reveal that of the s-electrons at the Fermi level, those of Al and Si have prevailing density of states and, thus predominantly contribute to the metallic conductivity. This also shows that the high residual resistivity of the materials studied is an intrinsic effect, not due to defects of the crystal structure.

The growth of SrRuO$_3$ (SRO) thin film with high-crystallinity and low residual resistivity (RR) is essential to explore its intrinsic properties. Here, utilizing the adsorption-controlled growth technique, the growth condition of initial SrO layer on TiO$_2$-terminated SrTiO$_3$ (STO) (001) substrate was found to be crucial for achieving a low RR in the resulting SRO film grown afterward. The optimized initial SrO layer shows a $c$(2 x 2) superstructure that was characterized by electron diffraction, and a series of SRO films with different thicknesses ($t$s) were then grown. The resulting SRO films exhibit excellent crystallinity with orthorhombic-phase down to $t \approx$ 4.3 nm, which was confirmed by high resolution X-ray measurements. From azimuthal X-ray scan for SRO orthorhombic (021) reflection, we uncover four structural domains with a dominant domain of orthorhombic SRO [001] along cubic STO [010] direction. The dominant domain population depends on $t$, STO miscut angle (${\alpha}$), and miscut direction (${\beta}$), giving a volume fraction of about 92 $\%$ for $t \approx$ 26.6 nm and (${\alpha}$, ${\beta}$) ~ (0.14$^{\rm o}$, 5$^{\rm o}$). On the other hand, metallic and ferromagnetic properties were well preserved down to $t \approx$ 1.2 nm. Residual resistivity ratio (RRR = ${\rho}$(300 K)/${\rho}$(5 K)) reduces from 77.1 for $t \approx$ 28.5 nm to 2.5 for $t \approx$ 1.2 nm, while ${\rho}$(5 K) increases from 2.5 $\mu\Omega$cm for $t \approx$ 28.5 nm to 131.0 $\mu\Omega$cm for $t \approx$ 1.2 nm. The ferromagnetic onset temperature ($T_c\prime$) of around 151 K remains nearly unchanged down to $t \approx$ 9.0 nm and decreases to 90 K for $t \approx$ 1.2 nm. Our finding thus provides a practical guideline to achieve high crystallinity and low RR in ultra-thin SRO films by simply adjusting the growth of initial SrO layer., Comment: 22 pages, 7 figures

We study the effect of addition of Ag on normal, paracoherent and superconducting coherent state of YBa2Cu3O7-δ (YBCO). We find that both room temperature resistivity and residual resistivity decrease with the addition of Ag in YBCO. In absence of magnetic field, the addition of Ag in YBCO shift various crossover temperatures of paracoherent state and 3D fluctuations dominate the mean-field region. However, the paracoherent state remains nearly unaffected in presence of 12 T magnetic field and 2D superconducting fluctuations dominate the mean-field region. The coherent state of YBCO improves by the addition of Ag in absence as well as in presence of 12 T magnetic field.

Parameters of the energy gap and, consequently, electronic, magnetic and galvanomagnetic properties in different X$_2$YZ Heusler alloys can vary quite strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless semiconductors (SGSs) with almost 100% spin polarization of charge carriers are promising materials for spintronics. The changes in the electrical, magnetic and galvanomagnetic properties of the Co$_2$YSi (Y = Ti, V, Cr, Mn, Fe) and Co$_2$MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF and/or SGS states were followed and their interconnection was established. Significant changes in the values of the magnetization and residual resistivity were found. At the same time, the correlations between the changes in these electronic and magnetic characteristics depending on the number of valence electrons and spin polarization are observed., 10 pages

We characterize low-loss electron-beam evaporated niobium thin films deposited under ultra-high vacuum conditions. Slow deposition yields films with a high superconducting transition temperature ($9.20 \pm 0.06 \rm ~K$) as well as a residual resistivity ratio of $4.8$. We fabricate the films into coplanar waveguide resonators to extract the intrinsic loss due to the presence of two-level-system fluctuators using microwave measurements. For a coplanar waveguide resonator gap of $2~\mu \rm m$, the films exhibit filling-factor-adjusted two-level-system loss tangents as low as $1.5 \times 10^{-7}$ with single-photon regime internal quality factors in excess of one million after removing native surface oxides of the niobium., Comment: 5 pages, 3 figures

Understanding the competition between superconductivity and other ordered states (such as antiferromagnetic or charge-density-wave (CDW) state) is a central issue in condensed matter physics. The recently discovered layered kagome metal AV3Sb5 (A = K, Rb, and Cs) provides us a new playground to study the interplay of superconductivity and CDW state by involving nontrivial topology of band structures. Here, we conduct high-pressure electrical transport and magnetic susceptibility measurements to study CsV3Sb5 with the highest Tc of 2.7 K in AV3Sb5 family. While the CDW transition is monotonically suppressed by pressure, superconductivity is enhanced with increasing pressure up to P1 ≈ 0.7 GPa, then an unexpected suppression on superconductivity happens until pressure around 1.1 GPa, after that, Tc is enhanced with increasing pressure again. The CDW is completely suppressed at a critical pressure P2 ≈ 2 GPa together with a maximum Tc of about 8 K. In contrast to a common dome-like behavior, the pressure-dependent Tc shows an unexpected double-peak behavior. The unusual suppression of Tc at P1 is concomitant with the rapidly damping of quantum oscillations, sudden enhancement of the residual resistivity and rapid decrease of magnetoresistance. Our discoveries indicate an unusual competition between superconductivity and CDW state in pressurized kagome lattice., The recently discovered kagome metal AV3Sb5 is a new playground to study the interplay between superconductivity and charge-density-wave (CDW) state. Here, the authors report pressure-dependent evolution of CDW and superconductivity in CsV3Sb5, suggesting an unusual competition between the two phases.

SrVO3 thin films with a high figure of merit for applications as transparent conductors were crystallized from amorphous layers using solid phase epitaxy (SPE). Epitaxial SrVO3 films crystallized on SrTiO3 using SPE exhibit a room temperature resistivity of 2.5 x 10-5 Ohms cm, a residual resistivity ratio of 3.8, and visible light transmission above 0.5 for a 60 nm-thick film. SrVO3 layers were deposited at room temperature using radio-frequency sputtering in an amorphous form and subsequently crystallized by heating in controlled gas environment. The lattice parameters and mosaic angular width of x-ray reflections from the crystallized films are consistent with partial relaxation of the strain resulting from the epitaxial mismatch between SrVO3 and SrTiO3. A reflection high-energy electron diffraction study of the kinetics of SPE indicates that crystallization occurs via the thermally activated propagation of the crystalline/amorphous interface, similar to SPE phenomena in other perovskite oxides. Thermodynamic calculations based on density functional theory predict the temperature and oxygen partial pressure conditions required to produce the SrVO3 phase and are consistent with the experiments. The separate control of deposition and crystallization conditions in SPE presents new possibilities for the crystallization of transparent conductors in complex geometries and over large areas., Comment: Keywords: epitaxial transparent conducting oxides, solid-phase epitaxy, strontium vanadate, phase selection in oxide synthesis