Superconducting Properties Research Articles

First principle calculation of electronic structures and hole concentration of YBCO family compounds

Yttrium barium copper oxide (YBCO) family compounds are similar in structure but have different superconducting temperatures. It is well known that superconducting properties arise from the crystal lattice and electronic structure of compounds. This work reveals and discusses the electronic structures of YBCO family compounds (YBa2Cu3O6, YBa2Cu3O6.5, YBa2Cu3O7, and YBa2Cu4O8) based on density functional theory (DFT). The electronic structure results show that Cu–O chains are the trigger components for conduction, and only Cu–O chains and Cu-O2 planes play important roles in electronic and superconducting properties. The results also reveal that additional hole doped will be non-trivially distributed between the Cu–O chains and the Cu-O2 planes, and hence a more comprehensive method is required to calculate the hole concentration in the Cu-O2 plane. This work also demonstrates the calculation of hole concentrations using DFT. By DFT calculation, the Y1236 has hole concentration of 0.5 and the hole doped of Y12365, Y1237 and Y124 are 0.09, 0.16 and 0.10, respectively. The results are consistent with the cuprate-superconductor phase diagram and the bond-valence sum (BVS) calculations.

Unified EOS incorporating the finite strain theory for explaining thermo elastic properties of high temperature superconductors, nanomaterials and bulk metallic glasses

In the present research paper, we have proposed a novel EOS, which is based on the concepts of finite strain theories for predicting the thermo elastic properties of various materials viz. bulk metallic glasses, nanomaterials, and high temperature superconductors. Development of the present EOS involved deriving an innovative mathematical framework that considers the effects of finite strain, enabling the prediction of essential properties like pressure and bulk modulus under different compression ratios. For validity and applicability of the proposed EOS, we have conducted an extensive analysis by comparing the calculated thermo elastic properties with existing theoretical models or equation of sates and experimental data available in the literature. The present comparison revealed a remarkable agreement between our predictions and the observed values for a wide range of compression of nanomaterials, bulk metallic glasses, and superconductors. Our research not only introduces a comprehensive equation of state for these advanced materials but also demonstrates its effectiveness in accurately capturing their unique thermodynamic behavior. This present derived EOS can serve as a valuable tool to predict and understand the response of nanomaterials, bulk metallic glasses, and superconductors to varying pressure conditions, aiding the design and development of innovative applications in fields such as materials science, nanotechnology, and condensed matter physics.

Discovery of Metastable W3P Single Crystals with High Hardness and Superconductivity.

Hard and superconducting materials play significant roles in their respective application areas and are also crucial research fields in condensed matter physics. Materials with the key properties of both hard and superconducting properties could lead to technology development, but it is also full of challenges. Herein, we report the synthesis of high-quality metastable W3P single crystals with superconductivity and excellent mechanical properties. The synergistic effect of temperature and pressure was effective in suppressing further decomposition of metastable W3P as-synthesized by our synthesis technique (high-pressure and high-temperature method). The transport and magnetic measurements indicate that W3P is a typical type-II BCS superconductor, displaying a superconducting transition temperature of 5.9 K and an impressive critical magnetic field of 4.35 T. Theory calculations reveal a metallic property in W3P, and the phonon modes of the vibration of W atoms are important for electron-phonon interaction. Meanwhile, W3P shows excellent mechanical properties with a high fracture toughness of 8 MPa m1/2 and an impressive asymptotic hardness of 22 GPa, which is currently reported as being the hardest among transition metal phosphides. It opens up a new class of advanced materials that combine excellent mechanical properties with superconductivity.

Competing length scales and 2D versus 3D dimensionality in relatively thick superconducting NbN films

Magneto-transport characteristics of 2D and 3D superconducting layers, in particular, temperature and angular dependences of the upper critical field Hc2, are usually considered to be fundamentally different. In the work, using non-local resistance measurements at temperatures near the normal-to-superconducting transition, we probed an effective dimensionality of nm-thick NbN films. It was found that in relatively thick NbN layers, the thicknesses of which varied from 50 to 100 nm, the temperature effect on Hc2 certainly pointed to the three-dimensionality of the samples, while the angular dependence of Hc2 revealed behavior typical for 2D samples. The seeming contradiction is explained by an intriguing interplay of three length scales in the dimensionally confined superconducting films: the thickness, the Ginzburg–Landau coherence length, and the magnetic-field penetration depth. Our results provide new insights into the physics of superconducting films with an extremely large ratio of the London penetration depth to the Ginzburg–Landau coherence length exhibiting simultaneously 3D isotropic superconducting properties and the 2D transport regime.

Superconductivity, quantum capacitance, and electronic structure investigation of transition metals (X = Y, Zr, Nb, Mo) encapsulated silicon nanoclusters (Si59X): Intuition from quantum and molecular mechanics

Silicon nanoclusters (SiNCs) have unique structural and electronic properties that make them promising candidates for energy storage devices such as batteries, supercapacitors, and solar cells. This study theoretically investigated the superconducting and capacitance properties of transition metal (TM) doped silicon nanoclusters using density functional theory (DFT) calculations. The electronic and ionic conductivity, as well as the non-linear optic property, of TM-doped silicon nanoclusters herein, were analyzed to determine their potential as capacitor electrodes. The effects of temperature on electronic and ionic conductivity were also studied. The results suggest that TM doping enhances the superconducting and capacitance properties of silicon nanoclusters. The electronic conductivity was found to increase with increasing temperature, while the ionic conductivity showed a nonlinear relationship with temperature. Furthermore, it was observed that the doping of studied certain TM elements, such as Nb and Mo, leads to the formation of metallic states within the HOMO-LUMO energy range, indicating their potential for superconducting behaviour. The HOMO-LUMO analysis also reveals the electronic band structure and the bandgap of TM-doped silicon nanoclusters, showing that the dopants can tune the bandgap, resulting in improved superconductivity capacitance. The NBO analysis reveals the nature of bonding between the dopant atoms and the silicon atoms, indicating that charge transfer between the dopants and the silicon atoms plays a crucial role in enhancing the electronic properties Additionally, the stability of TM-doped silicon nanoclusters was analyzed, and it’s found that the doping with TM elements resulted in stable structures. The result strongly suggested that doping with Y, Zr, Nb, and Mo enhances the capacitance at different voltages and conductivity at elevated temperatures especially as the electronic configuration of the d-orbital of the dopant evolves. Overall, this study provides valuable insights into the potential of TM-doped silicon nanoclusters as efficient materials for superconducting and capacitive applications.

First-principles insights on the A15 phase in Ti-Se system

A pressure-composition phase diagram of Ti-Se system has been established after a comprehensive computational study at high pressure. As the pressure increases to 72 GPa, a new A15 Ti3Se structure is predicted and it can be stabilized dynamically at zero pressure. We further investigate the electronic and superconducting properties of A15 Ti3Se. Due to the significant contribution of transition metal d electrons at the Fermi level, the phonon properties of the Ti-lattice considerably enter into the calculation of electron-phonon interactions. The calculated robust superconducting critical temperature Tc (μ∗= 0.10-0.15) is 26-21.34 K under 80 GPa. Our results may provide theoretical guidance for the discovery of other titanides at high pressure, facilitating the exploration of A15 superconductors in the form of A3B.

Superconducting properties and vortex pinning in intermetallic BaBi3 single crystals: A magnetization study

Hysteresis and magnetic relaxation measurements were performed on single crystals of BaBi3, which is an intermetallic compound exhibiting superconductivity with a critical temperature (Tc) of 5.9 K. The London penetration depth (λ) was determined to be 130 nm, and the coherence length (ξ) was estimated to be 13 nm. The critical current density (Jc) was found remarkably low, measuring 20,000 A/cm2 under self-field conditions at 1.8 K. Analysis of the pinning forces suggests vortex pinning by crystalline defects associated with volume Δk (variations in the Ginzburg-Landau parameter). The relaxation rate follows the Anderson-Kim model, and the pinning energies range from 1600 K at 0.02 T to 500 K at 0.5 T. Our study aims to advance our understanding of the connection between intrinsic superconducting properties and vortex behavior in intermetallic materials characterized by low thermal fluctuations.

Effect of pressure on superconductivity of LaBi3

The electronic properties, phonon properties, and conventional superconducting properties of the newly synthesized AuCu3-type intermetallic compound LaBi3 using first-principle density functional methods have been reported in this research article.Variations in conventional superconducting properties like transition temperature, electron–phonon coupling constant, Eliashberg spectral function and average logarithmic phonon frequency with applied hydrostatic pressure have been reported in this research article. At ambient pressure, the transition temperature and coupling constant was computed to be 7.2 K and 2.78 respectively. The calculated decrease in transition temperature with applied pressure as reported in this article agrees with the previously reported experimental results. Ambient pressure fermi surface was employed to explain the high electron–phonon coupling constant.

Proximity-induced superconductivity in type-II Weyl semimetal NbIrTe4

Heterostructures between conventional superconductors and materials with different electronic ground states have emerged as a powerful method for exploring the exotic superconducting properties induced by the proximity effect. Here, we investigate Andreev transport through the interface between an s-wave superconductor Nb and a type-II Wely semimetal NbIrTe4. The differential conductance measurement reveals an anomalous zero-bias conductance peak and prominent subgap structures at low temperatures. Furthermore, we found that these subgap structures are not only related to the interface coupling strength but also influenced by the thickness of the NbIrTe4 flake. For thin devices (≤100 nm), the differential conductance spectra only exhibit a single-gap structure. While in thicker devices (∼150 nm), we observed the distinct double-gap structure, which is likely to originate from the proximity-induced superconductivity gap on the bulk and surface of the NbIrTe4 flakes. These results can provide a good reference for understanding the superconducting phase in type-II Weyl semimetals and take a step toward its future application in the field of superconducting electronics.

Tallon's Equation and Its Parameters in Extreme Superconducting Alkali-Halides

In this research paper we have thoroughly investigated that Tallon's Equation and Its Parameters in Extreme Superconducting Alkali-Halides. Superconductivity, a quantum phenomenon characterized by the complete loss of electrical resistance, continues to captivate researchers due to its potential for transformative technological applications. In pursuit of a deeper understanding of superconducting materials, this research explores Tallon's Equation, a critical tool for predicting superconducting properties. Specifically, we investigate the applicability of Tallon's Equation to extreme conditions, particularly high temperatures and pressures, in alkali-halide compounds. This study combines theoretical modeling and experimental validation to assess the accuracy of Tallon's Equation in predicting key parameters of superconducting alkali-halides under extreme environments. We scrutinize alterations in transition temperature, critical magnetic fields, and other pivotal parameters as materials are subjected to high temperature and pressure regimes. Furthermore, this research extends beyond theoretical considerations to practical implications. It explores the potential of Tallon's Equation in guiding the design and development of novel superconducting materials optimized for high-pressure applications. The findings from this study hold promise for advancing our understanding of superconductivity and harnessing it for innovative technologies in fields such as energy transmission, magnetic resonance imaging, and beyond.

Multiple transition temperature enhancement in superconducting TiNbMoTaW high entropy alloy films through tailored N incorporation

We report about the influence of nitrogen incorporation on the superconducting transition temperature TC of TiNbMoTaW high entropy alloy films deposited using high power impulse magnetron sputtering. By measuring the temperature dependence of resistivity of (TiNbMoTaW)Nx nitrides, we observe a significant increase of TC, from 0.62 K for x = 0 up to 5.02 K for x = 0.74. With further increase of x, TC is decreasing and reaches 1.08 K for x = 0.97. The eightfold TC enhancement seems to be associated with the incorporation of light N atoms into the face-centered cubic lattice and with the x dependent enhancement of the electron-phonon interaction, which may be related to the high configuration entropy in high entropy alloys. Measurements in magnetic field show that the upper critical fields Bc2 of (TiNbMoTaW)Nx with x > 0.15 provide Bc2/TC > 2 T/K ratios, which are above the weak-coupling pair breaking limit. Additional heat capacity and point contact spectroscopy measurements show that the superconductivity in the ∼1 μm thick films is bulk in nature, consistent with conventional weak-coupling phonon mediated superconductivity. The proposed strategy of nitrogen incorporation into high entropy alloys may pave a pathway towards tailoring their superconducting properties, especially their TC.

Tuning the Fermi surface of PrSb to enhance the interplay between superconductivity and magnetism by Sn substitution

The nature of Fermi surface in view of shapes and density of the nearest energy bands plays important role in tuning the physical and chemical properties of heavy fermions, Weyl metals, topological insulators, and superconductors. The interplay between superconductivity, magnetism, and fermionic nature of materials can be enhanced by modifying the shape of Fermi surface. The modification may be accomplished by tuning the surface topology, such as flatness and thickness, of electronic energy bands around the Fermi surface. Herein, we investigate the interplay between the magnetism, superconductivity, and heavy Fermionic nature of PrSb by tuning the shape of the Fermi surface by Sn substitution via PrSnxSb1-x (x = 0.0,0.25,0.50,0.75 &1.0) substitution scheme. For the theoretical designing of the materials and computation of the targeted properties, we implement density functional theory using the generalized–gradient approximation extended to the Perdew-Bruke-Ernzerhof correction to account for the exchange–correlation. The modification in the thickness and flatness of energy bands and density of states around the Fermi surface of PrSb compounds by changing the Sn/Pb substitution ratio, leads to simultaneous enhancement of the interplay between magnetism, superconductivity, and fermionic nature of the compounds.

Tolerance to deformation and flux pinning in superconducting amorphous molybdenum nitride thin films grown on flexible polyimide

We investigate the superconducting properties of 80 nm thick amorphous MoNx films fabricated via reactive sputtering on silicon and flexible commercial polyimide substrates. The samples are grown at room temperature using reactive sputtering with a gas mixture of N2 and Ar. The mechanical deformation tolerance for films on polyimide is evaluated by comparing the superconducting critical temperature (Tc) and critical current density (Jc) when the films are attached to cooper surfaces with varying curvatures. The amorphous films exhibit a Tc of 8.2 K on silicon and 7.9 K on polyimide. Our results demonstrate a significant enhancement in flux pinning for the thin films grown on polyimide, with the Jc at self-field and 3 K increasing from approximately 0.5 MA/cm2 to around 1 MA/cm2. Analyses of Jc as a function of the magnetic field, angle, and temperature reveal that the films on polyimide exhibit remarkable resilience to deformation. Interestingly, comparable Jc values are observed when the samples are affixed to both flat and cylindrical surfaces with diameters of 2.5 cm. This observation suggests that vortex dissipation predominantly occurs through flux motion in the region experiencing the maximum Lorentz force. Furthermore, the films maintain Tc without any discernible changes in resistivity when fixed to cylindrical surfaces with 1.2 cm diameters. However, there is a significant drop in vortex pinning, indicating reduced pinning capability in the stressed regions. The high deformation tolerance of amorphous MoNx renders it highly suitable for cryogenic electronics applications, providing a viable alternative to the commonly utilized metallic Nb.

THE PENETRATION DEPTH OF H3S SUPERCONDUCTOR BY SEMICLASSICAL APPROACH

The penetration depth is a magnetic field mechanism by which an external magnetic field penetrates into superconductors’ surfaces and is related to the Meissner effect. The penetration depth property was studied by the semiclassical approach to identify other properties of superconductors. In this study, we investigated the penetration depth of the H3S superconductor under external pressure. The H3S superconductor is high Tc, s-wave isotropic, and high pressure prepared superconductors. We derive an analytical equation for the near-zero temperature penetration depth with pressure effect parameters. The derived equations were then numerically calculated and predicted the experimental data on H­3S superconductor penetration depth. We discovered that the temperature dependent penetration depth under pressure of H­3S superconductor is reasonable at Tc(χ = 473, ε0 = 91,Qp = 0.1) = 200.832 K. , as well as is the influence of the directly parameter on Tc(χ,ε0,Qp), Δ(0,χ,ε0,Qp), and λ(T,χ,ε0,Qp)/λ(0,χ,ε0,Qp), with Qp>0.1 does not corresponding theory

Anisotropy and isotope effect in superconducting solid hydrogen

Elucidating the phase diagram of solid hydrogen is a key objective in condensed matter physics. Several decades ago, it was proposed that at low temperatures and high pressures, solid hydrogen would be a metal with a high superconducting transition temperature. This transition to a metallic state can happen through the closing of the energy gap in the molecular solid or through a transition to an atomic solid. Recent experiments have managed to reach pressures in the range of 400–500 GPa, providing valuable insights. There is strong evidence suggesting that metallization via either of these mechanisms occurs within this pressure range. Computational and experimental studies have identified multiple promising crystal phases, but the limited accuracy of calculations and the limited capabilities of experiments prevent us from determining unequivocally the observed phase or phases. Therefore, it is crucial to investigate the superconducting properties of all the candidate phases. Recently, we reported the superconducting properties of the C2/c-24, Cmca-12, Cmca-4 and I41/amd-2 phases, including anharmonic effects. Here, we report the effects of anisotropy on superconducting properties using Eliashberg theory. Then, we investigate the superconducting properties of deuterium and estimate the size of the isotope effect for each phase. We find that the isotope effect on superconductivity is diminished by anharmonicity in the C2/c-24 and Cmca-12 phases and enlarged in the Cmca-4 and I41/amd-2 phases. Our anharmonic calculations of the C2/c-24 phase of deuterium agree closely with the most recent experiment by Loubeyre et al (2022 Phys. Rev. Lett. 29 035501), indicating that the C2/c-24 phase remains the leading candidate in this pressure range, and has a strong anharmonic character. These characteristics can serve to distinguish among crystal phases in experiment. Furthermore, expanding our understanding of superconductivity in pure hydrogen holds significance in the study of high-Tc hydrides.

THE STUDY ON TEMPERATURE-DEPENDENT SURFACE CRITICAL MAGNETIC FIELD OF IRON-BASED SUPERCONDUCTORS

The upper critical magnetic field (Hc2) is one of the important properties of superconductors in external magnetic field. The higher magnetic field strength, the more superconductivity is maintained. However, the surface critical magnetic field (Hc3) is larger than upper critical magnetic field which the ratio of Hc3 to Hc2 is constant. In this study, we investigated the surface critical magnetic field of the iron-based superconductor using Ginzburg-Landau’s anisotropic two-band method. The surface critical magnetic field was calculated with four temperature-dependent models. Our analytical formula of the surface critical magnetic field obtains the temperature parameters. Finally, the numerical calculation was applied to the experimental data of iron-based superconductors

Enhancement of critical current density and critical magnetic field of superconducting medium entropy alloy Nb2/5Hf1/5Zr1/5Ti1/5

We investigated the superconducting properties of medium entropy alloys (MEA) Nb2/5Hf1/5Zr1/5Ti1/5, synthesized by arc melting (AM) and powder metallurgical spark plasma sintering (SPS) methods. The samples exhibit superconducting transitions at Tc=7.99 K (AM) and 6.63 K (SPS) from the electrical resistivity measurements. The upper critical field at zero-temperature limit μoHc2(0) gives a relatively high value of 14.63 T (AM) and 11.68 T (SPS). The isothermal magnetic hysteresis of the SPS-MEA shows significantly enhanced vortex pinning, resulting in the enhancement of critical current density (Jc= 39,000 A/cm2) compared with the AM-MEA (Jc= 5,500 A/cm2) at 2 K (about seven times enhancement). The SPS-MEA shows a significant suppression of vortex avalanches compared with the previously reported SPS-HEA Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 superconductor. The SPS-MEA showed the secondary fishtail effect at a high magnetic field. There was a sizable specific heat jump ΔC(Tc)/γTc (3.3 for AM and 3.9 for SPS), significantly higher than the value of BCS prediction (1.43). Superconducting properties of MEA suggest the intermediate coupling of the electron-phonon coupling constant λ∼1 (λel−ph≃0.89 for AM and λel−ph≃0.78 for SPS) and the intermediate to strong coupling regime. The Kadowaki-Woods plot of the compounds is located on the line of the heavy fermion system. The Uemura plot indicates that the compounds are close to the conventional BCS superconductor. The contradictory property of strongly correlated and conventional BCS-type metallic superconductivity may come from the dirty superconducting regime with high Fermi velocity. Enhancing critical current density with significantly suppressed vortex avalanches on the SPS-MEA Nb2/5Hf1/5Zr1/5Ti1/5 compound suggests possible practical applications on the bulk superconductivity.

Atomic-scale electronic inhomogeneity in single-layer iron chalcogenide alloys revealed by machine learning of STM/S data

Chemical pressure from the isovalent substitution of Se by a larger Te atom in the epitaxial film of iron chalcogenide FeSe can effectively tune its superconducting, topological, and magnetic properties. However, such substitution during epitaxial growth inherently leads to defects and structural inhomogeneity, making the determination of alloy composition and atomic sites for the substitutional Te atoms challenging. Here, we utilize machine learning to distinguish between Se and Te atoms in scanning tunneling microscopy images of single-layer FeSe1−xTex on SrTiO3(001) substrates. Defect locations are first identified by analyzing spatial-dependent dI/dV tunneling spectra using the K-means clustering method. After excluding the defect regions, the remaining dI/dV spectra are further analyzed using the singular value decomposition method to determine the Se/Te ratio. Our findings demonstrate an effective and reliable approach for determining alloy composition and atomic-scale electronic inhomogeneity in superconducting single-layer iron chalcogenide films.

Induced delamination in REBCO coated-conductor tape by a scratch line and bending

The aim of this work is to study delamination promotion of the coated conductor (CC) tape under the influences of the scratches on the Ag surface when bending. For this purpose, the microstructural and superconducting properties of the CC tape bent in helical fashion with different former diameters were analyzed. Such CC tape that exhibits visible damage along its length in the form of “scratch line” caused on the final product was used. The CC tape was bent at a constant lay angle of 45° with a superconducting layer positioned inward to the former core experiencing compression. Transport current measurements in liquid nitrogen were performed to study superconducting properties of the CC tape.The results showed that delamination of the REBCO (Rare-Earth Barium Copper Oxide) layer started to form exclusively on the scratch location at tube diameter of 7 mm (corresponding to strain ε = −0.71 %) while the rest of the REBCO surface started to delaminate at tube diameter of 5 mm (ε = −0.99 %). As the superconducting properties of the CC tape are related with the REBCO delamination, the critical current degraded when first signs of REBCO delamination appeared as expected. Thus, it was observed that the scratches induce REBCO delamination during the bending process resulting in increase of critical bending radius.

Manufactured Yttrium Barium Copper Nano Oxide for Medicinal Applications

In light of the considerable interest surrounding the antibacterial properties of nanometal oxides and high-temperature superconductors, this study focuses on the synthesis of YBa2Cu3O7 (YBCO) using the Sol-Gel method. The research delves into the experimental aspects of nanoparticle (NP) synthesis and aims to elucidate the antibacterial potential of YBCO NPs, a high-temperature superconductor, against four distinct bacteria. These bacteria were subjected to varying concentrations of YBCO NPs (0.01 mg/ml, 0.025 mg/ml, 0.05 mg/ml, and 0.1 mg/ml). Comprehensive characterization of the synthesized nanoparticles encompassed techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. Remarkably, the Gram-positive strains, including Staphylococcus epidermidis and Methicillin-resistant Staphylococcus aureus (MRSA), exhibited pronounced susceptibility to the YBCO NPs, while Gram-negative strains displayed minimal response. Intriguingly, even at elevated concentrations of 0.01, 0.025, 0.05, and 0.1 mg/ml, these bacterial strains showcased resilient resistance. This research sheds light on the potential of YBCO NPs as an antibacterial agent against specific pathogens.