Behavior Of Superconductors Research Articles

Chemically tuning stability and superconductivity of Pd–H compounds: A routine to high temperature superconductivity under modest pressures

Motivated by searching room-temperature superconductors that could be realized near ambient conditions, palladium hydrides were chosen as the research subject considering that they can stably exist under ambient conditions, and Li as an electron donor for its outstanding performance in chemically tuning stability. A novel cubic phase structure of Li2PdH6 with a remarkably high estimated Tc of ∼165 K at 90 GPa was found using particle swarm optimization algorithm calculations. The superconducting behavior persists down to 10 GPa with a high Tc of 106.382 K. Even though the parent binary Pd–H system is not a good superconductor, the introduction of extra electrons breaks up the H2 molecules, inducing the increase of atomic hydrogen compared with parent hydride, which is necessary for outstanding superconducting behavior. The existence of relatively soft phonons associated with the H atoms in phonon dispersion curves is responsible for its high-Tc. Our results indicated that the doping of Li to binary hydrides, especially to binary hydrides with low-Tc that exist under ambient pressure, can produce robust phonon-mediated superconductivity. This may be a strategy to design and optimize room-temperature superconductors that can be synthesized under modest pressure. The findings may pave the way for realizing new high-Tc superconductors in experiments under lower pressure than recently documented superconducting hydrides.

Superconducting transition of GdBa2Cu3O7-x/La0.7A0.3MnO3 (A=Sr and Ca) bilayers governed by tunable interlayer structural coupling

Bilayers composed of high-Tc cuprate superconductors (HTS) with manganites have garnered significant attention due to the complex interaction between two layers, leading to competition among various ordering phenomena. When HTS and manganties are interfaced, new functionalities can emerge that are absent in the individual components. Notably, epitaxial strain can alter crystal structures and electronic states, significantly impacting superconductivity in HTS/manganite heterostructures. In this study, we analyze the superconducting and ferromagnetic behaviors of GdBa2Cu3O7-x(GdBCO)/La0.7A0.3MnO3(LAMO, where A=Sr and Ca) bilayers, maintain a constant GdBCO thickness of 500 nm while varying the LAMO thickness from 25 to 100 nm. We focus on the local structural correlations between the two layers. Temperature-dependent EXAFS spectra were systematically measured at the Cu and Mn K-edges to investigate the local atomic structures of both layers across the superconducting transition temperature (Tc). Our spectroscopic measurements reveal distinct conformations of the MnO6 octahedra near Tc, which are absent in single-layer LSMO, indicating structural coupling between the layers. Additionally, our magnetization studies show a strong relationship between the structural coupling, magnetic anisotropy (MA), and the superconducting transition of the GdBCO/LAMO bilayers. The additional distortion of the MnO6 octahedra in the GdBCO/LAMO bilayer, likely stemming from structural coupling, may account for the changes in the superconducting transition associated with magnetic anisotropy. This modification of structural coupling can be controlled by adjusting the LAMO thickness, yet it remains highly dependent on the bond geometry of LAMO. The Mn-O bond in LCMO is stiffer than in LSMO, resulting in a smaller change in structural coupling with varying thickness in LCMO compared to LSMO. The disparity in structural coupling directly impacts the magnetic properties of the LAMO layer and subsequently influences the superconducting property ΔTc. Our findings highlight the significance of structural coupling as a critical factor affecting the superconductivity of GdBCO/LAMO bilayers. Furthermore, this study provide foundational insight for designing various applications, such as magnetic sensors and spintronic devices, by enhancing our understanding of local dynamics at the interface between ferromagnets and superconductors.

Superconductivity and Mott Physics in Organic Charge Transfer Materials.

The phase diagrams of quasi two-dimensional organic superconductors display a plethora of fundamental phenomena associated with strong electron correlations, such as unconventional superconductivity, metal-insulator transitions, frustrated magnetism and spin liquid behavior. We analyze a minimal model for these compounds, the Hubbard model on an anisotropic triangular lattice, using cutting-edge quantum embedding methods respecting the lattice symmetry. We demonstrate the existence of unconventional superconductivity by directly entering the symmetry-broken phase. We show that the crossover from the Fermi liquid metal to the Mott insulator is associated with the formation of a pseudogap. The predicted momentum-selective destruction of the Fermi surface into hot and cold regions provides motivation for further spectroscopic studies. Our theoretical results agree with experimental phase diagrams of κ-BEDT organics.

Exploring the magnetic behavior of potassium-doped Cu0.5Tl0.5Ba2Ca2Cu3-xKxO10-δ (x=0, 1, 2.5, 3) superconductors

This study investigates the superconducting and magnetic behaviour of Potassium-doped Cu0.5Tl0.5Ba2Ca2Cu3-xKxO10-δ superconductors by varying potassium-concentrations (x = 0, 1, 2.5, 3). We have synthesized the samples by two-step solid-state-reaction method and explored their superconducting features by XRD analysis, SEM and resistivity measurements. Through a comprehensive exploration of magnetic measurements i.e magnetization versus magnetic field and temperature, we aim to elucidate the impact of potassium doping on the diamagnetic characteristics of these superconductors. The results reveal that by raising the doping concentration of potassium, the orthorhombic unit cell's axis lengths decresese. The onset of superconductivity and the magnitude of diamagnetism are also decreased. The magnetic behavior of these samples was studied by field cooled and zero field cooled from 2 to 300 K and taking the hysteresis loops at temperatures 2 to 60 K. In the doped samples, the suppression of current density is steeper with increase in temperature. Doped atoms boost the population of localized defects, which serve as pinning centers. This study will contribute valuable information to the understanding of the relationship between magnetic behavior and the superconducting nature of complex oxide materials.

Superconductivity and Metallic Behavior in Heavily Doped Bulk Single Crystal Diamond and Novel Transportation Behavior at Graphene/Diamond Heterostructure

AbstractOwing to extremely large bandgap of 5.5 eV and high thermal conductivity, diamond is recognized as the most important semiconductor. The superconductivity of polycrystalline diamond has always been reported, but there are also many controversies over the existence of superconductivity in bulk single crystal diamond. Besides, it remains a question whether a metallic state exists for such a large bandgap semiconductor. Herein, a single crystal superconducting diamond with a Hall carrier concentration larger than 3 × 1020 cm−3 is realized by co‐doped of boron and nitrogen, with an extremely low resistivity of 2.07 × 10−3 Ω cm at room temperature and dominated acceptor–donor bounded exciton photoluminescence. Furthermore, it is shown that diamond can transform from superconducting to metallic state under similar carrier concentration with tuned carrier mobility degrading from 9.10 cm2 V−1 s−1 or 5.30 cm2 V−1 s−1 to 2.66 cm2 V−1 s−1 or 1.34 cm2 V−1 s−1. Through integrating graphene on a nitrogen and boron heavily co‐doped diamond, a novel transportation behavior in the monolayer graphene similar with superconducting behavior is realized through combining Andreev reflection and exciton‐mediated superconductivity, which may reveal more interesting superconducting behavior of diamond.

Precision Control of Amphoteric Doping in Cu x Bi2Se3 Nanoplates.

Copper-doped Bi2Se3 (Cu x Bi2Se3) is of considerable interest for tailoring its electronic properties and inducing exotic charge correlations while retaining the unique Dirac surface states. However, the copper dopants in Cu x Bi2Se3 display complex electronic behaviors and may function as either electron donors or acceptors depending on their concentration and atomic sites within the Bi2Se3 crystal lattice. Thus, a precise understanding and control of the doping concentration and sites is of both fundamental and practical significance. Herein, we report a solution-based one-pot synthesis of Cu x Bi2Se3 nanoplates with systematically tunable Cu doping concentrations and doping sites. Our studies reveal a gradual evolution from intercalative sites to substitutional sites with increasing Cu concentrations. The Cu atoms at intercalative sites function as electron donors while those at the substitutional sites function as electron acceptors, producing distinct effects on the electronic properties of the resulting materials. We further show that Cu0.18Bi2Se3 exhibits superconducting behavior, which is not present in Bi2Se3, highlighting the essential role of Cu doping in tailoring exotic quantum properties. This study establishes an efficient methodology for precise synthesis of Cu x Bi2Se3 with tailored doping concentrations, doping sites, and electronic properties.

Exploring the Coexistence Conditions and Intrinsic Relationships between Electrides, Superconductivity, Kagome Lattice, and Superionic Behaviors in Li–Ge Compounds

Exploring the Coexistence Conditions and Intrinsic Relationships between Electrides, Superconductivity, Kagome Lattice, and Superionic Behaviors in Li–Ge Compounds

Competition between d-wave superconductivity and magnetism in uniaxially strained Sr2RuO4

The pairing symmetry of Sr2RuO4 is a long-standing fundamental question in the physics of superconducting materials with strong electronic correlations. We use the functional renormalization group to investigate the behavior of superconductivity under uniaxial strain in a two-dimensional realistic model of Sr2RuO4 obtained with density functional theory and incorporating the effect of spin-orbit coupling. We find a dominant dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{{{{\\rm{x}}}}}^{2}-{{{{\\rm{y}}}}}^{2}}$$\\end{document} superconductor mostly hosted by the dxy-orbital, with no other closely competing superconducting state. Within this framework, we reproduce the experimentally observed enhancement of the critical temperature under strain and propose a simple mechanism driven by the density of states to explain our findings. We also investigate the competition between superconductivity and spin-density wave ordering as a function of interaction strength. By comparing theory and experiment, we discuss constraints on a possible degenerate partner of the dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{{{{\\rm{x}}}}}^{2}-{{{{\\rm{y}}}}}^{2}}$$\\end{document} superconducting state.

Intercalation based synthesis of Chevrel phase superconductors

This work focuses on the superconducting and magnetic properties of Chevrel phase (CP) compounds (Cu2Mo6S8 and Ni2Mo6S8) processed via a novel self-propagating high-temperature synthesis (SHS) method involving ternary cation intercalation in MoS2 high-temperature polymorphs. Green pellets of the precursor materials sealed under vacuum and exposed to 1050 °C or 1200 °C rapidly transformed from a powder mixture into submicron CPs within minutes. X-ray diffraction analysis confirmed the presence of Cu2Mo6S8 CP (67%), and Ni2Mo6S8 (93%). This group has illustrated the first time CP were formed at low energy cost and full stoichiometry. Magnetization versus temperature data obtained for the samples under different field conditions confirmed the superconducting behavior of the Cu–CP at a critical temperature of 8.3 K. The Ni–CP behaved as a superparamagnetic at low temperature (4.2 K). The results of this work suggest that the novel SHS process offers a viable scalable synthesis route for the Chevrel family of compounds and that it is worth exploring the functional applications of the new compounds of this material system.

Enhancing electric field calculation in HTS tape simulations for currents exceeding the critical limit using full HTS tape modeling

Superconducting devices are an interesting technological option for improvement of efficiency of energy systems. High-temperature superconducting tapes are among the best choices for power applications. Because of their high non-linearity, the design of devices with superconducting tape requires specific simulation models and methods to correctly represent the superconducting behavior. The J-A formulation has been investigated as an efficient tool to represent the electromagnetic behavior of such devices. It is based on the current density (J) and magnetic vector potential (A), and able to represent both superconducting materials and ferromagnetic materials. With regards to the tapes, the use of thin-film approximation can be successful with the J-A formulation. Usually, only representations considering the superconducting layer of tapes have been investigated. This becomes a problem for operations where the current in the superconductor surpasses the critical current, for example in transient analysis. This paper presents an analysis of the effects the inclusion of all of the tapes’ layers have on simulations with the J-A formulation with thin-film approximations. By considering all layers of the tape, one represents the transition between superconducting and high-loss states of the tape. A simple system, consisting of a single tape with applied current, has been studied as benchmark and simulated with J-A and the more established T-A formulation in two cases: considering all layers; and only the superconducting layers. Results show that results for the J-A and T-A formulations are compatible and the inclusion of all layers improves the stability of the simulation and provides correct assessment of the electric field in the tapes.

Electronic Band Structure and Fermi Surface Analysis of Ce2 Ni1-Xcoxge2: A Pseudo Potential Study

This study uses pseudopotential calculations to investigate the electronic band structure and Fermi surface properties of Ce2Ni1-xCoxGe2 alloys. The research problem centers on understanding the effects of Co substitution on the electronic properties of these alloys, particularly regarding potential high-temperature superconducting behavior. The methodology involves density of states (DOS) analysis and Fermi surface calculations for Ce2Ni1-xCoxGe2 alloys with varying Co concentrations. Results reveal a notable increase in DOS around the Fermi level with increasing Co substitution, indicative of enhanced metallic behavior and potential superconducting characteristics. Additionally, band structure analyses demonstrate the significant role of hybridization between Ce 4f, Ni/Co 3d, and Ge 4s/4p orbitals in determining electronic behavior. Fermi surface calculations unveil a transition from near-spherical to complex 2D and 3D shapes with higher Co concentrations, suggesting modifications in Fermi energy surface nestings or electron scattering. This study's conclusions emphasized the intricate electronic structure of Ce2Ni1-xCoxGe2 alloys and highlighted the potential for further exploration in high-temperature super conductivity research.

On-device phase engineering.

In situ tailoring of two-dimensional materials' phases under external stimulus facilitates the manipulation of their properties for electronic, quantum and energy applications. However, current methods are mainly limited to the transitions among phases with unchanged chemical stoichiometry. Here we propose on-device phase engineering that allows us to realize various lattice phases with distinct chemical stoichiometries. Using palladium and selenide as a model system, we show that a PdSe2 channel with prepatterned Pd electrodes can be transformed into Pd17Se15 and Pd4Se by thermally tailoring the chemical composition ratio of the channel. Different phase configurations can be obtained by precisely controlling the thickness and spacing of the electrodes. The device can be thus engineered to implement versatile functions in situ, such as exhibiting superconducting behaviour and achieving ultralow-contact resistance, as well as customizing the synthesis of electrocatalysts. The proposed on-device phase engineering approach exhibits a universal mechanism and can be expanded to 29 element combinations between a metal and chalcogen. Our work highlights on-device phase engineering as a promising research approach through which to exploit fundamental properties as well as their applications.

Electronic, optical, and thermoelectric characteristics of (Ae)xFBiS2 (Ae=Sr, Ba, and x=1.7) layered materials useful in optical modulator devices

The recent discovery of superconductivity behavior in the mother BiS2-layered compounds has captivated the attention of several physicists. The crystal structure of superconductors with alternate layers of BiS2 is homologous to that of cuprates and Fe-based superconductors. The full-potential linearized augmented plane-wave (FP-LAPW) technique was utilized to investigate the electronic structures and density of states in the vicinity of the Fermi energy of SrFBiS2 and BaFBiS2 compounds under the electron carriers doping. The introduction of electron doping (carries doping) reveals that the host compounds SrFBiS2 and BaFBiS2 exhibit features indicative of superconductivity. This carrier doping of SrFBiS2 and BaFBiS2 compounds (electron-doped) has a significant impact on the lowest conduction states near the Fermi level for the emergence of the superconducting aspect. The electron doping modifies and induces changes in the electronic structures with superconducting behavior in (Ae)1.7FBiS2(Ae=Sr,Ba) compounds. A Fermi surface nesting occurred under the modification of electrons (carriers) doping in the host compounds SrFBiS2 and BaFBiS2. Furthermore, the optical characteristics of the carrier-doped SrFBiS2 and BaFBiS2 compounds are simulated. Due to the anisotropic behavior, the optical properties of these materials based on BiS2 demonstrate a pronounced polarization dependency. The starting point at zero photon energy in the infrared region is elucidated by considering the Drude features in the optical conductivity spectra of SrFBiS2 and BaFBiS2 compounds, when the electron carriers doping is applied. It was clearly noticed that the spin-orbit coupling (SOC) influences the electronic band structures, density of states, Femi surface, and optical features because of the heavy Bismuth atom, which may disclose fascinating aspects. Further, we conducted simulations to assess the thermoelectric properties of these mother compounds. The two BiS2-layered compounds could be suitable for practical thermoelectric purposes and are highlighted through assessment of electrical conductivity, thermal conductivity, Seebeck coefficient, and power factor. As a result, we propose that the mechanisms of superconducting behavior in BiS2 family may pave new avenues for investigating the field of unconventional superconductivity. It may also provide new insights into the origin of high-Tc superconductivity nature.

First-principles calculations on mechanical and electronical properties of AlB[formula omitted]-type CaB[formula omitted]

In the present study, we focused on studying the properties of CaB2 in the hexagonal AlB2-phase. To determine the characteristics of the material, it is crucial to use first-principles calculation methods. Therefore, we used the Density Functional Perturbation Theory to calculate the elastic constants, phonon frequencies, and electron–phonon coupling properties of CaB2, which are important for understanding its superconducting and mechanical behaviors. Additionally, we analyzed Fermi surfaces and electronic band structures and compared them to those of MgB2. Our calculations showed that there is a close relationship between electron–phonon coupling and the superconducting properties of the material. We discovered that the critical superconducting transition temperature value is 24.71 K. In a remarkable finding, the presence of a Dirac cone at the Fermi level was observed in the electronic band structure, which may indicate that the material may be a topological semi-metal.

Superconductivity and superionic behaviors of Kagome lattices in Li–Si compounds under high pressure

P–T phase diagrams of the superconducting, solid, superionic, and liquid states in the Li5Si-P6/mmm at 50 and 100 GPa.

Theoretical investigation of structural instabilities of newly predicted superconducting Heusler alloys Rh2NbZ (Z = Al, Ga, Sn): Ab initio approach

We systematically investigate the structural and elastic properties of Rh2NbZ (Z = Al, Ga, Sn) through ab initio calculations. We determine the equilibrium lattice parameters in the cubic austenitic phase of Rh2NbZ and observe martensitic structural transitions in all compositions. These transitions are attributed to the lone pair effect of s electrons on the Z element, leading to a paramagnetic ground state for all alloys. In addition, we discover superconducting behavior of Rh2NbZ, as evident from the total density of states plots. Furthermore, we calculate various elastic parameters in cubic phase to understand the structural stability.

Chemical composition effect on superconductivity in noncentrosymmetric [formula omitted]-Mn-type high-entropy alloys

We report the effect of chemical composition variation on the superconductivity in noncentrosymmetric β-Mn-type high-entropy alloys (HEAs) studied in two very similar Ta5+xMo35−xW5Re35Ru20C20 and Ta5+yW35−yMo5Re35Ru20C20 series. It is found that both HEAs consist of a single cubic β-Mn-type phase for 0 ≤x≤ 6 and 0 ≤y≤ 9. Bulk fully gapped superconductivity is observed for all these HEAs and their zero-temperature upper critical fields approach the Pauli paramagnetic limit. While our analysis suggests that Tc of these HEAs is mainly controlled by the electron–phonon coupling strength, Tc of the Ta5+xMo35−xW5Re35Ru20C20 series is always higher than that of the Ta5+yW35−yMo5Re35Ru20C20 one even for (nearly) the same valence electron concentration and unit-cell volume. This difference is attributed to the different contributions of Mo and W to the electronic structure, which is supported by the first-principles calculations. Our study suggests that the chemical composition effect should be considered to better understand the superconducting behavior in noncentrosymmetric HEAs.

Synthesis and characterization of niobium carbide thin films on diamond surface for superconductive application

Diamond's unique properties make it attractive for use in a variety of industrial applications. However, this material has not found mass application in microelectronics due to several factors, including the lack of large-sized plates, n-type doping, and high-quality metallization. In this article, we address the problem of diamond surface metallization by forming niobium carbide layers. We obtained a niobium carbide film several nanometers thick that exhibits superconducting behavior up to 12.4 K. To our knowledge, this is the highest superconducting transition temperature achieved in the niobium carbide system. The crystal lattice parameter of the film is 4.4659 Å, which is close to the maximum value for niobium carbide lattice parameters. Density functional theory calculations were employed to investigate the thermodynamic stability of niobium carbide compounds at various temperatures and determine the superconducting critical temperature of niobium carbide. The combination of diamond's high thermal conductivity, along with the strong adhesion and superconductivity of niobium cabide films, introduces exciting possibilities for the realization of superconductive sensitive detectors.

Magnetic ac susceptibility of superconducting Ta films for quantum computing

Recently, breakthroughs were reported in the long coherence time (>0.5 ms) transmon qubit using tantalum films (Ta). Identifying the loss mechanism in Ta films will help further improve the performance of Ta-based superconducting qubits. Here, we report a study of superconducting properties in two sets of Ta films grown on c-cut and a-cut sapphires respectively using contact transport and noncontact magnetic ac susceptibility measurements. Although the resistive transition appears to be similar in both films, we found strikingly different responses in their complex magnetic susceptibilities . in the c-cut films exhibits a sharp peak at superconducting transition T c and becomes featureless below T c indicating a strongly coupled superconducting state. In contrast, in the a-cut films exhibits a broad peak near T c and a second peak appears below T c, indicating granular superconductivity behavior. This second peak in is associated with the hysteresis loss at weak-link-type grain boundaries, which is believed to be a leading source of decoherence in the a-cut Ta films. The derived magnetic loss tangent in the a-cut films is about one order of magnitude higher than in the c-cut films. This study demonstrates that ac susceptibility is an excellent probe for characterizing bulk superconducting properties of the constituent superconducting materials used in qubits.

Role of a capping layer on the crystalline structure of Sn thin films grown at cryogenic temperatures on InSb substrates

Metal deposition with cryogenic cooling is a common technique in the condensed matter community for producing ultra-thin epitaxial superconducting layers on semiconductors. However, a significant challenge arises when these films return to room temperature, as they tend to undergo dewetting. This issue can be mitigated by capping the films with an amorphous layer. In this study, we investigate the influence of different in situ fabricated caps on the structural characteristics of Sn thin films deposited at 80 K on InSb substrates. Regardless of the type of capping, we consistently observe that the films remain smooth upon returning to room temperature and exhibit epitaxy on InSb in the cubic Sn (α-Sn) phase. Notably, we identify a correlation between alumina capping using an electron beam evaporator and an increased presence of tetragonal Sn (β-Sn) grains. This suggests that heating from the alumina source may induce a partial phase transition in the Sn layer. The existence of the β-Sn phase induces superconducting behavior of the films by percolation effect. This study highlights the potential for tailoring the structural properties of cryogenic Sn thin films through in situ capping. This development opens avenues for precise control in the production of superconducting Sn films, facilitating their integration into quantum computing platforms.