Residual Resistivity Research Articles (Page 1)

At temperatures T much lower than its superconducting critical temperature Tc = 2.1 K, the heavy fermion superconductor UTe2 has a unique phase diagram of magnetic field H vs. φ and θ, angles H is tilted from the b-axis toward the a- and c-axes, respectively, of its orthorhombic unit cell. The phase diagram contains three distinct superconducting phases: SC1 in which φ and θ extend from 0 to 90° and H ≤ ~15 T; SC2 for φ ≤ ~7°, θ ≤ ~4° and ~15 T ≤ H ≤ Hm = ~35 T, the onset of the magnetic field polarized (FP) phase, and SCFP which resides entirely within the FP phase in a pocket of superconductivity extending from θ ≈ 20° to 40° and from ~40 T to above 60 T. We studied the evolution of the H vs. θ phase diagram for Th concentrations 0.005 ≤ x ≤ 0.047 in the U1-xThxTe2 system at ~0.6 K. Within this range of x values, SC1 extends over 0 ≤ θ ≤ 90° and H ≤ ~10 T for x = 0.047, while SC2 is suppressed. The SCFP and FP phases are unaffected to x = 0.02 but are completely suppressed in the region x = 0.025 to 0.047 where the residual resistance ratio RRR ~3 indicates a significant amount of disorder. These results complement recent studies of nonsuperconducting disordered UTe2 single crystals in which the SC1 and SC2 phases are absent, but the FP and so-called "orphan" SCFP phases are retained.

Abstract Epitaxial thin films of the heavy fermion compound YbRh2Si2 have opened new possibilities in the investigation of the enigmatic strange metal state, including terahertz transmission spectroscopy and shot noise. For experiments at lower temperatures and energies, further advances in film quality are desirable. In this work, The focus is on the enhancement of crystallinity and surface smoothness of YbRh2Si2 thin films grown by molecular beam epitaxy using Knudsen cells and electron‐beam evaporation sources. The morphology is influenced by the Yb flux and provides insight into the crystal quality of the thin films confirmed by in‐plane and out‐of‐plane diffraction techniques. Changes in the surface morphology affect the physical characteristics of the film. A nucleation study is performed with the assistance of ab initio calculations of the binding energy of each element, i.e., Yb, Rh, and Si, with the substrate and permits to further reduce the surface roughness of the films and refinement of crystal quality, as evidenced by sharper peaks in X‐ray diffraction scans. The residual resistance ratio depends linearly on the lattice mismatch. At low temperatures, the electrical resistivity of the best epitaxial thin films exhibits a linear‐in‐temperature dependence characteristic of strange metals.

The origin of large magnetoresistance (MR) in WTe2 has been extensively debated, with electron–hole compensation initially proposed as the dominant mechanism. Herein, we systematically investigate the magnetotransport properties of mechanically exfoliated WTe2 nanoflakes. A well-developed quadratic MR is observed, which cannot be explained by electron–hole compensation because the ratio of electron to hole concentration is greater than unity. Instead, the MR exhibits a strong correlation with the residual resistivity ratio, indicating disorder as a key factor. Considering the carrier inhomogeneity induced by disorder, we find that the quadratic MR follows a universal scaling behavior with the ratio of carrier concentration to its fluctuation, consistent with the effective-medium theory. These findings highlight the dominance of disorder in generating the large quadratic MR in WTe2 nanoflakes.

Ternary transition metal (TM) nitrides have gained significant attention in thin film research due to their promising properties for a broad range of applications. Particularly, some of the ternary TM nitrides have been predicted to adopt layered structures that make them interesting for thermoelectric conversion and quantum materials applications. Unfortunately, synthesis of TM ternary nitride films by physical vapor deposition often favors disordered 3D structures rather than the predicted 2D-like layered structure. In this study, we investigate the structural interplay in the Sc-Ta-N ternary system using a combinatorial approach. Combinatorial libraries ScxTa1−xN are synthesized following a two-step method: First, deposit film precursors by cosputtering and then process the resulting 3D-structured samples with rapid thermal annealing. Synchrotron grazing-incidence wide-angle x-ray scattering on films annealed at 1200∘C for 20 min leads to the nucleation of ScTaN2 layered structure (P63/mmc) near stoichiometry. We find that the layered structure can accommodate large off-stoichiometry in the Ta-rich region (x<0.5), facilitated by the alloying with quasi-isostructural Ta5N6 compound that exists on a composition tie line at x=0. While focusing on ScTaN2, we estimate the long-range order parameter in near-stoichiometric films to be 0.86, corresponding to a fraction of Sc/Ta antisites of 7%. Transport measurements on ScTaN2 reveal a nearly temperature-independent high carrier density (1021cm−3), suggesting a heavily doped semiconductor or semimetallic character, consistent with a small positive Seebeck coefficient of +19 µV/K. The carrier mobility at 2 K is relatively small (9.5cm2V−1s−1) and the residual-resistivity ratio is minor, suggesting that electrical conduction is dominated by defects or disorder. Measured magnetoresistance suggests possible weak antilocalization at 2 K. This paper highlights the interplay between ScTaN2 and Ta5N6 crystal structures in stabilizing layered materials, emphasizes the importance of cation order/disorder for potential tunable alloys, and suggests that ScTaN2 is a promising platform for exploring electronic properties.

Mutual control of critical temperature, residual resistance ratio, stress, and roughness for sputtered Nb films

This work aimed at better understanding the origins of electrical resistivity in Ag-based thermal control glazings. To do so, the temperature-dependent resistivity (4-300 K) of model ZnO/Ag(12 nm)/ZnO sputter-deposited stacks was carefully analyzed using the Mayadas-Shatzkes model [Mayadas, A. F.; Shatzkes, M. Phys. Rev. B 1970, 1, 1382], in parallel to their microstructure (grain size, mosaicity, interface roughness), and epitaxial orientation studied by X-ray diffraction and electron microscopy. By using different substrates (glass versus single crystal), Ag film seed layers, or even deposition machines, by changing the nature of interfaces and by annealing, strong differences in terms of metal crystallinity could be achieved at constant thickness. ZnO/Ag/ZnO stacks are characterized by a hexagon/hexagon/hexagon epitaxial relationship leading to a strong Ag[111] out-of-plane texture. A peculiar attention was brought to resistivity fits by fixing grain size, thickness, and intragrain residual resistivity to extract the electron reflection coefficient R at grain boundaries and the interface scattering parameter p. These quantities were systematically correlated to the film microstructure obtained from X-ray diffraction. Beyond grain size, the analysis showed a noticeable difference between single crystal (R ≃ 0)- and glass (R ≃ 0.15)-based stacks and a counterintuitive increase of R upon annealing. Both findings were explained by the intrinsic link between R and the film texture or average grain boundary angle. Interfaces were found to strongly scatter electrons with p ≃ 0.1-0.4, but no clear-cut correlation could be established with the roughness derived from X-ray reflectivity (XRR). Rather strong changes in p could be achieved by varying the interface nature or by annealing. These findings were tentatively explained by changes in the electronic characteristics of the interface. At last, the intrinsic violation of the Matthiessen rule showed that disentangling intragrain, grain boundary, and interface contributions to film resistivity is deceptive, at least for the studied thickness.

Abstract We study the thermodynamics and phase stability of the AlTiVNb and AlTiCrMo refractory high-entropy superalloys using a combination of ab initio electronic structure theory—namely a concentration wave analysis—and atomistic Monte Carlo simulations. Our multiscale approach is suitable both for examining atomic short-range order in the solid solution, as well as for studying the emergence of long-range crystallographic order with decreasing temperature. In both alloys considered in this work, in alignment with experimental observations, we predict a B2 (CsCl) chemical ordering emerging at high temperatures, which is driven primarily by Al and Ti, with other elements expressing weaker site preferences. The predicted B2 ordering temperature for AlTiVNb is higher than that for AlTiCrMo. These chemical orderings are discussed in terms of the alloys’ electronic structure, with hybridisation between the sp states of Al and the d states of the transition metals understood to play an important role. Within our modelling, the chemically ordered B2 phases for both alloys have an increased predicted residual resistivity compared to the A2 (disordered bcc) phases. These increased resistivity values are understood to originate in a reduction in the electronic density of states at the Fermi level, in conjunction with qualitative changes to the alloys’ smeared-out Fermi surfaces. These results highlight the close connections between composition, structure, and physical properties in this technologically relevant class of materials.

We present a study of the low-temperature, high-field magnetotransport behavior of epitaxially grown CrO2 thin films on (100) TiO2 substrates. Electron transport measurements confirm high sample quality, with a residual resistivity ratio as large as 45. A logarithmic fit of the low-temperature regime yields a T4.5 power law, indicative of the elusive double-magnon scattering in half-metallic ferromagnets. Angle-dependent anisotropic magnetoresistance (AMR) measurements reveal a large projected density of states along [001] with a maximum AMR value of 2.4%. Pronounced, axis-dependent Shubnikov–de Haas (SdH) oscillations are observed in the longitudinal magnetoresistance (MR), with discrete Landau levels mapped at various tilt angles of the magnetic field. Their angular dependence follows a 1/cosθ relation pointing to a highly anisotropic Fermi surface, and amplitude scaling adheres closely to the thermodynamic Lifshitz-Kosevich formalism. The out-of-plane MR reaches 6.58%, the largest reported for CrO2 thin films. Notably, this study presents an observation of SdH oscillations in a half-metallic oxide with near-perfect spin polarization, a significant advancement in the field of spintronics.

The growth of superconducting tantalum nitride (TaN) thin films on magnesium oxide (MgO) substrates has been studied using pulsed laser deposition (PLD). This research investigates the influence of varying deposition parameters, including substrate temperature and ambient gas composition, on the structural, morphological, and superconducting properties of the films. X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy analyses revealed that the TaN films exhibit excellent crystallinity and smooth surface morphology, when deposited at optimal temperatures of 750 and 850 °C. The films exhibit superconducting transition temperatures (T c) ranging from 5.0 to 6.3 K, depending on the stoichiometry and deposition conditions. Resistance-temperature curves further confirm the high quality of the films, as evidenced by their low residual resistivity ratios. These findings demonstrate that PLD is a suitable technique for producing high-quality TaN superconducting films.

In the rapidly evolving field of quantum computing, niobium nitride (NbN) superconductors have emerged as integral components due to their unique structural properties, including a high superconducting transition temperature (Tc), exceptional electrical conductivity, and compatibility with advanced device architectures. This study investigates the impact of high-temperature annealing and high-dose gamma irradiation on the structural, electrical, and superconducting properties of NbN films grown on GaN via reactive DC magnetron sputtering. The as-deposited cubic δ-NbN (111) films exhibited a high intensity distinct x-ray diffraction (XRD) peak, a high Tc of 12.82 K, and an atomically flat surface. Annealing at 500 and 950 °C for varying durations revealed notable structural and surface changes. High-resolution scanning transmission electron microscopy (STEM) indicated improved local ordering, while atomic force microscopy showed reduced surface roughness after annealing. X-ray photoelectron spectroscopy revealed a gradual increase in the Nb/N ratio with higher annealing temperatures and durations. High-resolution XRD and STEM analyses showed lattice constant modifications in δ-NbN films, attributed to residual stress changes following annealing. Additionally, XRD φ-scans revealed a sixfold symmetry in the NbN films due to rotational domains relative to GaN. While Tc remained stable after annealing at 500 °C, increasing the annealing temperature to 950 °C degraded Tc to 8.7 K and reduced the residual resistivity ratio from 0.85 in the as-deposited films to 0.29 after 30 min annealing. The effects of high-dose gamma radiation [5 Mrad (Si)] were also studied, demonstrating minimal changes to crystallinity and superconducting performance, indicating excellent radiation resilience. These findings highlight the potential of NbN superconductors for integration into advanced quantum devices and its suitability for applications in radiation-intensive environments such as space, satellites, and nuclear power plants.

We report evidence for superconductivity with onset temperatures up to 11 K in thin films of the infinite-layer nickelate parent compound NdNiO2. A combination of oxide molecular beam epitaxy and atomic hydrogen reduction yields samples with high crystallinity and low residual resistivities, a substantial fraction of which exhibit superconducting transitions. We survey a large series of samples with a variety of techniques, including electrical transport, scanning transmission electron microscopy, x-ray absorption spectroscopy, and resonant inelastic x-ray scattering, to investigate the possible origins of superconductivity. We propose that superconductivity could be intrinsic to the undoped infinite-layer nickelates but suppressed by disorder due to a possibly sign-changing order parameter, a finding which would necessitate a reconsideration of the nickelate phase diagram. Another possible hypothesis is that the parent materials can be hole doped from randomly dispersed apical oxygen atoms, which would suggest an alternative pathway for achieving superconductivity.

Abstract The ternary transition-metal telluride TaCo2Te2 has been reported to host a topological band structure characterized by a nontrivial Berry phase. While transport properties have been investigated in both bulk crystals and thick flakes (>150 nm), studies on thin flakes (＜100 nm) of this van der Waals (vdW) material remain scarce. We investigate the low-temperature transport properties of TaCo2Te2 thin flakes by fabricating Hall bar devices on mechanically exfoliated flakes with different thicknesses (15 nm and 90 nm). Temperature-dependent resistance measurements reveal that the 15-nm-thick sample exhibits a lower residual resistivity ratio and Debye temperature compared to the 90-nm-thick one. Magnetotransport measurements under perpendicular magnetic fields up to ±14 T demonstrate lower magnetoresistance, carrier concentration, and mobility in the thinner sample, suggesting increased phonon scattering due to defect-induced disorder. Remarkably, pronounced Shubnikov-de Haas (SdH) oscillations are observed above 8 T in both samples in spite of the defect-induced disorder. Analysis of the Landau fan diagram yields a non-zero Berry phase in both samples, indicating the existence of a topologically non-trivial phase in TaCo2Te2 thin flakes. Our findings establish TaCo2Te2 as a promising candidate for exploring intrinsic topological states in layered materials.

Abstract Magnetoresistance (MR) stands as a pivotal transport phenomenon within the realm of condensed matter physics. In recent years, materials exhibiting extremely large unsaturated magnetoresistance (XMR), which are often potential topological materials, have garnered significant attention. In this study, we synthesized single crystal of ZrBi2 and performed electrical and specific heat measurements on them. The resistivity of ZrBi2 displays metallic behavior with a high residual resistance ratio (RRR). Notably, the MR of ZrBi2 reaches approximately 2.0 × 103% at 2 K and 16 T without saturation. Weak Shubnikov-de Haas (SdH) oscillations with two frequencies were observed above 13.5 T, which correspond to 237 T and 663 T. Hall effect fitting yields nearly equal concentrations of electron and hole carriers with the concentrations approximately 1021 cm-3 and the mobilities approximately 5000 cm2·V-1·s-1 at 2 K. The XMR could be attributed to the compensation of electron-hole with high mobility.

Chromium nitride (CrN), with its near room-temperature antiferromagnetic transition, is regarded as a promising candidate for next-generation spintronic devices. While epitaxial CrN films have been successfully synthesized via pulsed laser deposition, growing high-quality CrN films using magnetron sputtering (a widely applied technique for large-scale fabrication) remains a big challenge. In this work, we develop a method to synthesize high-quality epitaxial CrN films by a homemade 90° and 40° off-axis magnetron sputtering epitaxy. The residual resistivity ratio of these CrN films is around 3.28, one of the highest values in reports. Moreover, the effects of different sputtering setups (90° and 40° off-axis) on the physical properties of the CrN films were systematically investigated. It is shown that both CrN films have high crystallinity, superior conductivity (σ ∼ 6200 S/cm), and robust near room-temperature (TN ∼ 270 K) Néel transitions. Compared to the CrN films grown by the 40° off-axis sputtering, the CrN films synthesized by the 90° off-axis sputtering have higher Néel temperatures (276 K) and carrier mobility (77 cm2 V−1 s−1). Our work provides a way to synthesize high-quality CrN films by magnetron sputtering epitaxy and uncovers the effects of the off-axis sputtering geometry on the physical properties of films.

Extremely large magnetoresistance (XMR) is typically observed in topological materials as associated with factors such as high mobility carriers and electron-hole compensation. However, its occurrence in magnetic materials is rather rare due to the stability of the electron spin in magnetic fields. In this study, the synthesis of high-quality single crystals of Fe2Ge3 with the highest residual resistivity ratio (RRR = 4778) has allowed to explore its intrinsic magnetic and electrical transport properties, revealing a narrow-gap semiconductor nature with a high XMR of 2057% at 1.8 K and 12 T. In addition, Fe2Ge3 is able to bridge the gap between magnetism and XMR. These findings not only advance our understanding of Fe2Ge3, but also open avenues for the development of spintronic devices and other technologies based on magnetic semiconductors.

We report on the observation of a flat band situated at the Fermi levelEFalong with the structural, electrical transport, and magnetic properties of BaCo2P2that crystallizes in the ThCr2Si2-type body-center tetragonal structure. This compound has the largest inter-layer pnictide (Pn) distancedPn-Pnas well as the largestc/aratio among all the knownACo2Pn2(A= alkaline earth metal) compounds, whereaandcare the tetragonal lattice parameters. Hence, the magnetic and electronic properties of this compound are expected to have a quasi-two-dimensional character. Despite the evidence of the presence of sizable magnetic interactions, magnetic susceptibilityχ(T)of BaCo2P2does not show magnetic ordering down to 1.8 K. The material shows good metallic conduction with a large residual resistivity ratioρ300K/ρ1.8K≈70and a Fermi liquid behavior at low temperature. Kadowaki-Woods ratioRKWof BaCo2P2suggests the presence of sizable electronic correlations within this system. Additionally, a large many-body enhancement of 2.3 of the experimental density of statesDγ(EF)over the band-structureDband(EF)is inferred to arise from sizable electron-electron and/or electron-phonon interactions leading to a substantial deviation from the free-electron behavior.

Abstract This article reports the synthesis of single crystalline gray-Arsenic (As) via the Bismuth flux method. The X-ray Diffraction (XRD) pattern revealed the single phase of the as-grown crystal, which crystallized in the rhombohedral structure with the space group R-3m. The sharp XRD peaks observed on mechanically exfoliated thin flakes of the same ensured high crystallinity of the same with growth direction along the c-axis. The Energy Dispersive X-ray Analysis (EDAX) endorses the stoichiometric purity of the as-grown As single crystal. The Raman spectra are recorded to study the vibrational mode, which showed peaks at 196.2cm-1 and 255.74cm-1, identified as Eg and A1g modes, respectively, by DFT calculations. The as-grown crystal is further characterized for its electronic and magneto-transport properties. The resistivity vs. temperature (ρ-T) measurements illustrated its metallic nature throughout, right from 300K down to 2K. The measured residual resistivity ratio (ρ300K/ ρ2K) of the sample is 180, which endorses the high metallic nature of the as-synthesized As single crystal. The transverse magnetic field-dependent resistivity (ρ-H) measurements elucidated huge (104%) magneto-resistance (MR) at 2K and 14Tesla transverse magnetic fields, along with the SdH oscillations, indicating the presence of topological surface states. The non-trivial band topology and edge states in As are confirmed by first principle calculations. Not only do orbital projected bands show the signature of band inversion, but also the Z2 invariant value (1,111) calculated by Wilson’s loop method affirms As to be a strong topological insulator (TI). Clear evidence of topological edge states in plane kz = 0 has been observed in surface state spectra and slab bands.

Residual resistance ratio measurement system for Nb3Sn wires extracted from Rutherford cables

Abstract Superconductors exhibit dissipationless supercurrents even under finite bias and magnetic field conditions, provided these remain below the critical values. However, type-II superconductors in the flux flow regime display Ohmic dissipation arising from vortex dynamics under finite magnetic fields. The interplay between supercurrent and Ohmic dissipation in a type-II superconductor is dictated by vortex motion and the robustness of vortex pinning forces. In this study, we present an experimental investigation of the superconducting phase transitions and vortex dynamics in the atomically thin type-II superconductor 2H-NbSe2. We fabricated a high-quality multilayer 2H-NbSe2 with a step junction, demonstrating supercurrent in clean limit below a critical temperature of 6.6 K and a high residual resistance ratio of 17. The upper critical field was estimated to be 4.5 T and the Ginzburg–Landau coherence length 8.6 nm. Additionally, we observed phase transitions induced by vortex viscous dynamics in the 2H-NbSe2 step junction. Analysis of the pinning force density using the Dew-Hughes model indicates that the pinning force in the 2H-NbSe2 device can be attributed to step junction, related to the surface-Δκ type of pinning centers. Our findings pave the way for engineering pinning forces by introducing artificial pinning centers through partial atomic thickness variation in layered 2D superconductors while minimizing unwanted quality degradation in the system.

To study diffusion characteristics in substitutional f.c.c.-Ni–Al alloys, we review, analyse, and use the kinetic models, in which the relaxation of correlation parameters for the atomic distribution causes the time dependence of both the diffuse-scattering intensity I and the residual electrical resistivity ρ. Using the parameterization of the available literature data about the measurement of the residual electrical resistivity during the isothermal annealing of alloys, the most characteristic relaxation times of ρ after quenching of the alloys and its equilibrium value ρ∞ are estimated. The maximum characteristic relaxation time of the atomic order of such alloys is determined, and the curves of the time dependence of the normalized change in intensity ΔI are predicted based on the hypothesis of the coincidence of the largest characteristic relaxation times for I and ρ. The relaxation process is accompanied by both the increase in the number of clusters with the presence of short-range order in their structure and the degree of their order that is consistent with both the results of computer modelling of local atomic ordering using the Monte Carlo method and the model of inhomogeneous short-range order.