Residual Resistivity Research Articles

Structural, Magnetic, and Electrical Properties and Magnetoresistance of Monovalent K-Substituted La0.7Ba0.3−xKxMnO3 (x = 0 and 0.04) Manganite

The effects of K+ substitution at the Ba-site on the structural, magnetic, and electrical properties and magnetoresistance (MR) of La0.7Ba0.3−xKxMnO3 (x = 0 and 0.04) manganites prepared via the solid-state method were investigated. Rietveld refinement of X-ray diffraction data confirmed that both samples were crystallized in the rhombohedral structure with the R3c¯ space group. In addition, the unit cell volume, V, and the average grain size also increased with K+ ions. Magnetization versus applied field (M–H) measurement was carried out, and the saturation magnetization (Ms) was found to increase from 1.81 μB/f.u. (x = 0) to 4.11 μB /f.u. (x = 0.04), implying that K+ ions strengthened the ferromagnetic (FM) interaction. Furthermore, the metal–insulator transition temperature, TMI, increased from 257 K (x = 0) to 271 K (x = 0.04). The observed behaviour may be related to the enhancement of double-exchange (DE) interaction due to the increase in Mn-O-Mn bond angle and electronic bandwidth (W), favouring the increasing rate of the eg electron hopping process. The fitting of the electrical resistivity data in the metallic region describes the significance of residual resistivity, electron–electron and electron–magnon scattering processes to elucidate the electronic transport properties. Within the insulating region, variable range hopping (VRH) and small polaron hopping (SPH) models are proposed to describe the conduction mechanism.

Bayesian optimization with experimental failure for high-throughput materials growth

A crucial problem in achieving innovative high-throughput materials growth with machine learning, such as Bayesian optimization (BO), and automation techniques has been a lack of an appropriate way to handle missing data due to experimental failures. Here, we propose a BO algorithm that complements the missing data in optimizing materials growth parameters. The proposed method provides a flexible optimization algorithm that searches a wide multi-dimensional parameter space. We demonstrate the effectiveness of the method with simulated data as well as in its implementation for actual materials growth, namely machine-learning-assisted molecular beam epitaxy (ML-MBE) of SrRuO3, which is widely used as a metallic electrode in oxide electronics. Through the exploitation and exploration in a wide three-dimensional parameter space, while complementing the missing data, we attained tensile-strained SrRuO3 film with a high residual resistivity ratio of 80.1, the highest among tensile-strained SrRuO3 films ever reported, in only 35 MBE growth runs.

First Observation of the de Haas–van Alphen Effect and Fermi Surfaces in the Unconventional Superconductor UTe2

We report the first observation of the de Haas–van Alphen (dHvA) effect in the novel spin-triplet superconductor UTe2 using high quality single crystals with a high residual resistivity ratio (RRR) over 200. The dHvA frequencies, named α and β, are detected for the field directions between c- and a-axes. The frequency of branch β increases rapidly with the field angle tilted from c- to a-axis, while branch α splits, owing to the maximal and minimal cross-sectional areas from the same Fermi surface. Both dHvA branches, α and β reveal two kinds of cylindrical Fermi surfaces with a strong corrugation at least for branch α. The angular dependence of the dHvA frequencies is in very good agreement with that calculated by the generalized gradient approximation (GGA) method taking into account the on-site Coulomb repulsion of U = 2 eV. It indicates that the main Fermi surfaces are experimentally detected. The observed cyclotron effective masses are large in the range from 32 to 57 m0. They are approximately 10–20 times lager than the corresponding band masses, consistent with the mass enhancement obtained from the Sommerfeld coefficient, γ and the calculated density of states at the Fermi level. The local density approximation (LDA) calculations of ThTe2 assuming U4+ with the 5f2 localized model are in less agreement with our experimental results, in spite of the prediction for two cylindrical Fermi surfaces, suggesting a mixed valence states of U4+ and U3+ in UTe2.

The Effect of Different Copper Discs on the Discharge of Superconducting Coils

High temperature superconducting (HTS) magnets often work at high energy density and have slow quench propagation speed, so a quench will present a serious risk to the safety of magnets. The quench protection method based on the dump resistance can effectively reduce the current and release the energy in the HTS magnets. However, too large dump resistance may cause excessive voltage across the magnets. A quench protection system consisting of dump resistances and metal discs has been proposed. Copper discs are often embedded in HTS magnets for conducting cooling and mechanical support. In the discharging process of HTS magnets, the copper discs can absorb energy from the magnets through magnetic coupling, thus accelerating the current decay of the magnets. This quench protection method is more effective than using dump resistance alone. In this paper, the effect of different copper discs on the discharging process of HTS coils is discussed. Eight types of copper with different residual resistivity ratios (RRR) are applied. The results show that with the increase of the RRR of the copper disc, the current decay rate of the coil increases, and the energy absorbed by the copper disc from the coil increases. The role of different copper discs in the fast quench protection of the coil can be sorted as: RRR = 300 > RRR = 100 > RRR = 80 > RRR = 60 > RRR = 40 > RRR = 30 > RRR = 20 > RRR = 10. The copper disc with RRR of 300 shows the best performance in quench protection of HTS coils.

Observation of quantum criticality in antiferromagnetic based (Ce1Y )2Ir3Ge5 Kondo-Lattice system

• The chemical substitution dependencies of the three power law parameters have very similar behavior. • The minimum n exponent, maximum A coefficient, and ρo residual resistivity are at the same critical concentration x cr , expecting the sign for QCP in a non-Fermi Liquid (nFL) region. • Above x cr , the A values drop abruptly and the n values increase only slightly, indicating a transition from strongly to weakly correlated regime near the critical concentration x cr . We have carried out a detailed study of the (Ce 1 −x Y x ) 2 Ir 3 Ge 5 anti-ferromagnetic compounds across the entire range of substitution 0 ≤ x ≤ 0.33 and report the results of powder X-ray diffraction, magnetic susceptibility, heat capacity, and electrical resistivity measurements to exhibit the anti-ferromagnetic phase temperature ( T N ) versus substitution x phase diagram. The pure Ce 2 Ir 3 Ge 5 system indicates anti-ferromagnetic behavior below T N = 9.5 K. Substitution of Y into (Ce 1 −x Y x ) 2 Ir 3 Ge 5 compound leads to a decrease in the anti-ferromagnetic phase temperature ( T N ). Near x = 0.3, the anti-ferromagnetic transition temperature is suppressed to zero kelvin at an apparent anti-ferromagnetic quantum critical point, without the superconductivity sign, where the temperature dependence of the heat capacity and electrical resistivity in this region reveal non-Fermi Liquid behavior. The above results, for example, the suppressing of T N, maybe a new way to find low-temperature superconductivity in these compounds.

Single crystal growth of superconducting UTe2 by molten salt flux method

The molten salt flux method is applied as a synthetic route for the single crystals of the spin-triplet superconductor ${\mathrm{UTe}}_{2}$. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at ${T}_{\mathrm{c}}=2.1\phantom{\rule{4pt}{0ex}}\mathrm{K}$, which is the highest ${T}_{\mathrm{c}}$ reported for this compound. The obtained crystals show a remarkably large residual resistivity ratio with respect to the room temperature value and a small residual electronic contribution in specific heat well below ${T}_{\mathrm{c}}$. These results indicate that the increase of ${T}_{\mathrm{c}}$ in ${\mathrm{UTe}}_{2}$ can be achieved by reducing the disorder associated with uranium vacancies. The excess uranium in the molten salt acts as a reducing agent, preventing tetravalent uranium from becoming pentavalent and suppressing creation of uranium vacancies. At the same time, the relatively low growth temperature can suppress Te volatilization.

EFFECT OF LATTICE MISMATCH ON THE MICROSTRUCTURE AND ELECTRICAL PROPERTIES OF LaNiO3 CONDUCTIVE FILMS

In this work, we prepared LaNiO3 (LNO) and Au-LaNiO3 (Au-LNO) films using sol–gel multilayer coating method. The effects of lattice mismatch on the microstructure and electrical properties of the films were investigated by choosing different single-crystal substrate. XRD, SEM, and AFM results showed the high quality of LNO and Au-LNO films, indicating the successful epitaxial growth of the films on the single-crystal substrates. The room temperature resistivity of LNO films increased with the increase of lattice mismatch while different tendency was observed in Au-LNO films, suggesting that different mechanisms prevailed in the LNO and Au-LNO films. Both the transport behavior and the residual resistivity ratio were checked to explore the relationship between the lattice mismatch and the electrical properties of the films. Strain and defect concentration were proposed as the predominating factors for the changes in the resistivity of LNO and Au-LNO films under the influence of lattice mismatch.

Evaluation and degradation mechanism of residual performance of RC beam after drop hammer impact

The residual load-carrying performance after impact is a key index to evaluate the impact-resistant capacity of engineering-used structure member. A multi-functional experimental facility was developed to conduct both the impact test and post-impact static loading test on two types of flexural-failure-dominated RC beam specimens with different tensile reinforcement ratios. Three-dimensional nonlinear finite element(FE) analysis was conducted to reproduce the impact process and to investigate the plastic damage of RC beam in depth. The degradation mechanism of load-carrying performance of RC beam after impact was investigated through fiber-section analysis with uniaxial damaged material models of concrete and reinforcement. The experimental and numerical results demonstrate that the resistance and stiffness of impact-damaged RC beam decrease in different levels. The residual flexural resistance and stiffness ratios are greatly affected by the longitudinal reinforcements. The yield state of compressive reinforcements plays critical effect on the residual performance of RC beam after impact.

Material Properties of a Low Contraction and Resistivity Silicon–Aluminum Composite for Cryogenic Detectors

We report on the cryogenic properties of a low-contraction silicon–aluminum composite, namely Japan Fine Ceramics SA001, to use as a packaging structure for cryogenic silicon devices. SA001 is silicon–aluminum composite material (75% silicon by volume) and has a low thermal expansion coefficient ( $$\sim $$ 1/3 that of aluminum). The superconducting transition temperature of SA001 is measured to be 1.18 K, which is in agreement with that of pure aluminum and is thus available as a superconducting magnetic shield material. The residual resistivity of SA001 is 0.065 µΩm, which is considerably lower than equivalent silicon–aluminum composite material. The measured thermal contraction of SA001 immersed in liquid nitrogen is $$\frac{L_{293\,\mathrm {K}}-L_{77\,\mathrm {K}}}{L_{293\,\mathrm {K}}}=0.12\%$$ , which is consistent with the expected rate obtained from the volume-weighted mean of the contractions of silicon and aluminum. The machinability of SA001 is also confirmed with a demonstrated fabrication of a conical feedhorn array, with a wall thickness of 100 µm. These properties are suitable for packaging applications for large-format superconducting detector devices.

Impact of silver addition on the superconducting performances of Bi2Sr2Ca0.925Na0.075Cu2Oy:Ag composite fibers

This work studies the impact of metallic Ag addition on the microstructural, electrical, superconducting, and magnetic properties of Bi2Sr2Ca0.925Na0.075Cu2Oy. Samples with 0, 1, 3, 5 wt% were prepared from precursors produced by sol-gel method, followed by texturing through the laser floating zone (LFZ) technique. The normal state and residual resistivity values decrease with Ag addition up to 3 wt% (from 7.61 to 2.54, and from 1.85 to 0.25 mΩ.cm, respectively), reflecting the reduction of porosity and the improvement of grains alignment and connectivity. Irreversibility line (IL) shifts towards high temperature with the introduction of Ag, confirming the higher grains connectivity in Ag-containing samples. Moreover, the increase of Hirr (from 28.9 to 43.1 T), Hc2 (from 64.6 to 85.9 T), and Jc (from 4×104 to 1.2×105 A/cm2) values with Ag addition also point out to the improvement of grains connectivity and flux pinning energies induced by Ag addition.

Structural defects in compounds ZnXSb (X=Cr, Mn, Fe) : Origin of disorder and its relationship with electronic properties

Crystallographic disorder is known to be crucial for the understanding of transport properties of intermetallic compounds. ZrSiS-type phases with the general formula ZnXSb, where X is a transition metal, are recognized for their extraordinarily large amount of structural defects. Here, we explain the origin of the disorder and investigate its influence on the electronic behavior of ZnCrSb, ZnMnSb, and ZnFeSb. Synchrotron diffraction data revealed substantial amounts of vacancies on the transition-metal sites for all three compounds. Based on bonding analysis and calculations of crystal orbital Hamilton population (COHP), we claim that the defects originate from antibonding interactions on a two-dimensional square sublattice formed by X atoms. To test our thesis, we compare the ZrSiS-type materials with the chemically similar phase, ZnNiSb, which crystallizes in the MgAgAs-type cell. In this structure, the closest X-X distance is almost doubled with respect to the ZrSiS-type counterparts. In concert with expectations, the COHP calculation for ZnNiSb does not show an X-X antibonding interaction, and virtually no defects are detectable via the experimental diffraction analysis. From the perspective of electron transport, ZrSiS-type compounds were characterized by a residual resistivity ratio (RRR) that was significantly lower than that of ZnNiSb, which indicates stronger point-defect scattering of electrons in our disordered compounds. At the lowest temperatures, we also observed, for ZrSiS-type compounds, signatures of another phenomenon known exclusively for disordered metallic conductors: the Altshuler-Aronov (AA) correction to Coulomb interaction. The effect is not present for the defect-free compound ZnNiSb. ZnFeSb shows the lowest RRR and the highest onset temperature of the AA effect. Furthermore, heat-capacity studies revealed order of magnitude enhancement of Sommerfeld coefficient for ZnFeSb with respect to the value obtained from ab initio density of states calculations. This finding might be correlated to the structural instability. The presented analysis can be useful for understanding materials in which structural disorder significantly affects the electronic properties.

Resistivity and thermal conductivity of an organic insulator β′–EtMe3Sb[Pd(dmit)2

A finite residual linear term in the thermal conductivity at zero temperature in insulating magnets indicates the presence of gapless excitations of itinerant quasiparticles, which has been observed in some candidate materials of quantum spin liquids (QSLs). In the organic triangular insulator β′–EtMe3Sb[Pd(dmit)2]2, a QSL candidate material, the low-temperature thermal conductivity depends on the cooling process and the finite residual term is observed only in samples with large thermal conductivity. Moreover, the cooling rate dependence is largely sample dependent. Here we find that, while the low-temperature thermal conductivity significantly depends on the cooling rate, the high-temperature resistivity is almost perfectly independent of the cooling rate. These results indicate that in the samples with the finite residual term, the mean free path of the quasiparticles that carry the heat at low temperatures is governed by disorders, whose characteristic length scale of the distribution is much longer than the electron mean free path that determines the high-temperature resistivity. This explains why recent X-ray diffraction and nuclear magnetic resonance measurements show no cooling rate dependence. Naturally, these measurements are unsuitable for detecting disorders of the length scale relevant for the thermal conductivity, just as they cannot determine the residual resistivity of metals. Present results indicate that very careful experiments are needed when discussing itinerant spin excitations in β′–EtMe3Sb[Pd(dmit)2]2.

Anomalous transport in high-mobility superconducting SrTiO3 thin films.

The study of subtle effects on transport in semiconductors requires high-quality epitaxial structures with low defect density. Using hybrid molecular beam epitaxy (MBE), SrTiO3 films with a low-temperature mobility exceeding 42,000 cm2 V−1 s−1 at a low carrier density of 3 × 1017 cm−3 were achieved. A sudden and sharp decrease in residual resistivity accompanied by an enhancement in the superconducting transition temperature were observed across the second Lifshitz transition where the third band becomes occupied, revealing dominant intraband scattering. These films further revealed an anomalous behavior in the Hall carrier density as a consequence of the antiferrodistortive (AFD) transition and the temperature dependence of the Hall scattering factor. Using hybrid MBE growth, phenomenological modeling, temperature-dependent transport measurements, and scanning superconducting quantum interference device imaging, we provide critical insights into the important role of inter- versus intraband scattering and of AFD domain walls on normal-state and superconducting properties of SrTiO3.

Single thermodynamic transition at 2 K in superconducting UTe2 single crystals

UTe2 is a newly-discovered unconventional superconductor wherein multicomponent topological superconductivity is anticipated based on the presence of two superconducting transitions and time-reversal symmetry breaking in the superconducting state. The observation of two superconducting transitions, however, remains controversial. Here we demonstrate that UTe2 single crystals displaying an optimal superconducting transition temperature at 2 K exhibit a single transition and remarkably high quality supported by their large residual resistance ratio and small residual heat capacity in the superconducting state. Our results shed light on the intrinsic superconducting properties of UTe2 and bring into question whether UTe2 is a multicomponent superconductor at ambient pressure.

Electron beam evaporation of superconductor-ferromagnet heterostructures

We report on the electronic and magnetic properties of superconductor-ferromagnet heterostructures fabricated by electron beam evaporation on to unheated thermally oxidised Si substrates. Polycrystalline Nb thin films (5 to 50 nm thick) were shown to possess reliably high superconducting critical temperatures (T_{c}), which correlate well with the residual resistivity ratio (RRR) of the film. These properties improved during ex-situ annealing, resulting in {Delta }T_{c} and {Delta }RRR increases of up 2.2 K (sim 40% of the pre-annealed T_{c}) and 0.8 (sim 60% of the pre-annealed RRR) respectively. Nb/Pt/Co/Pt heterostructures showed substantial perpendicular anisotropy in the ultrathin limit (≤ 2.5 nm), even in the extreme limit of Pt(0.8 nm)/Co(1 nm)/Pt(0.6 nm). These results point to the use of electron beam evaporation as route to line-of-sight deposited, low-thickness, high quality Nb-based superspintronic multilayers.

Fabrication of surface ion traps with integrated current carrying wires enabling high magnetic field gradients

A major challenge for quantum computers is the scalable simultaneous execution of quantum gates. One approach to address this in trapped ion quantum computers is the implementation of quantum gates based on static magnetic field gradients and global microwave fields. In this paper, we present the fabrication of surface ion traps with integrated copper current carrying wires embedded inside the substrate below the ion trap electrodes, capable of generating high magnetic field gradients. The copper layer’s measured sheet resistance of 1.12 mΩ/sq at room temperature is sufficiently low to incorporate complex designs, without excessive power dissipation at high currents causing a thermal runaway. At a temperature of 40 K the sheet resistance drops to 20.9 μΩ/sq giving a lower limit for the residual resistance ratio of 100. Continuous currents of 13 A can be applied, resulting in a simulated magnetic field gradient of 144 T m−1 at the ion position, which is 125 μm from the trap surface for the particular anti-parallel wire pair in our design.

Thermal conductivity of niobium and thermally sprayed copper at cryogenic temperature

We have developed a test facility dedicated to thermal conductivity k(T) measurements at low temperature. These experimental devices allow the test of four samples simultaneously during each run. The measurements are performed using steady-state axial heat flow method with a careful control of heat leaks to the surrounding. The apparatus was successfully used for measuring k(T) (Temperature T in the range: 1.5 K - 10 K) of niobium and other materials used for the fabrication of Superconducting Radio Frequency (SRF) cavities. We have tested the following samples: 1) niobium samples from different supplier (as received or/and after various high temperature Heat Treatments (HT)), 2) thermally sprayed copper coatings. The resulting experimental data are presented and compared to the experimental results previously reported by other groups and theoretical values. As expected heat treatment have a strong impact on k(T) and in particular on the phonons peak at T∼2K. More precisely, HT @ 1200°C with Ti gettering improves the Nb Residual Resistance Ratio (RRR) by a factor of 3 and consequently k(T). Finally, the correlation between the niobium RRR and the thermal conductivity. at T=4.2 K is confirmed in good agreement with the Wiedemann-Franz law

Low-Temperature Thermal Conductivity of the Two-Phase Superconductor CeRh2As2

CeRh2As2is a rare unconventional superconductor (Tc= 0.26 K) characterized by two adjacent superconducting phases for a magnetic fieldH‖c-axis of the tetragonal crystal structure. Antiferromagnetic order, quadrupole-density-wave order (T0= 0.4 K) and the proximity of this material to a quantum-critical point have also been reported: The coexistence of these phenomena with superconductivity is currently under discussion. Here, we present thermal conductivity and electrical resistivity measurements on a single crystal of CeRh2As2between 60 mK and 200 K and in magnetic fields (H‖c) up to 8 T. Extrapolation of our normal-state data to zero temperature validates the Wiedemann-Franz law within the error bars. TheTdependence of the thermal conductivityκ(T) shows a pronounced drop belowTcwhich is also field dependent and thus interpreted as the signature of superconductivity. However, the large residual resistivity and the lack of sharp anomalies inκ(T) at the expected transition temperatures clearly indicate that samples of much higher purity are required to gain more information about the superconducting gap structure.

Physical properties and electronic structure of single-crystal KCo2As2

We present a method for producing high quality $\mathrm{K}{\mathrm{Co}}_{2}{\mathrm{As}}_{2}$ crystals, stable in air and suitable for a variety of measurements. X-ray diffraction, magnetic susceptibility, electrical transport, and heat capacity measurements confirm the high quality and an absence of long range magnetic order down to at least 2 K. Residual resistivity values approaching 0.25 $\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}$ cm are representative of the high quality and low impurity scattering, and a Sommerfeld coefficient $\ensuremath{\gamma}=7.3 \mathrm{mJ}/\mathrm{mol}$ ${\mathrm{K}}^{2}$ signifies weaker correlations than the Fe-based counterparts. Together with Hall effect measurements, angle-resolved photoemission experiments reveal a Fermi surface consisting of electron pockets at the center and corner of the Brillouin zone, in line with theoretical predictions and in contrast to the mixed carrier types of other pnictides with the $\mathrm{Th}{\mathrm{Cr}}_{2}{\mathrm{Si}}_{2}$ structure. A large, linear magnetoresistance of 200% at 14 T, together with an observed linear and hyperbolic, rather than parabolic, band dispersions are unusual characteristics of this compound.

Electronic scattering in half-Heusler thermoelectrics from resistivity data

A key part of optimising thermoelectric materials is understanding the electronic scattering mechanism. For half-Heusler (HH) thermoelectrics, the dominant mechanisms are acoustic phonon scattering in pure systems and alloy scattering in highly alloyed systems. In this report, the significance of the residual resistivity ρ 0 is highlighted. Large ρ 0 values can lead to misidentification of the dominant scattering mechanism when only high-temperature ρ(T) data is available. A straightforward approach to analyse ρ(T) is proposed and applied to a range of HH systems. This reveals large levels of structural disorder in XIVNiSn, whilst XVFeSb has the strongest coupling with acoustic phonons. The electronic scattering mechanism depends sensitively on composition, with acoustic (ρ sim T 1.5), metallic (simT 1) and alloy (simT 0.5) scattering observed within the main HH families. With the aid of velocity of sound, band mass and carrier concentration data, the deformation potential can be obtained, enabling quantification of the interaction between phonons and carriers, from fits to resistivity data. This work provides a route for the analysis of experimental ρ(T) data that can be applied to a range of thermoelectric materials.