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The binary high-pressure phase diagram of the Ta–Sb system was constructed for the first time in this study, utilizing the evolutionary algorithm USPEX and density functional theory (DFT). Ten pressurized dynamically and mechanically stable or metastable novel phases of Ta–Sb were discovered, including I4/mmm-TaSb2, P4/nmm-TaSb, P-3-Ta2Sb7, I4/mmm-Ta2Sb3, P-4m2-Ta7Sb, Pm-3-Ta7Sb, Pmm2-Ta15Sb, P4/nmm-TaSb3, I4/mmm-Ta3Sb4, and I4/mmm-Ta2Sb5. The compounds P-4m2-Ta7Sb and Pmm2-Ta15Sb exhibit promising characteristics as non-centrosymmetric superconductors (NCSs), with their superconducting critical temperature (TC) being 3.831 and 3.221 K, respectively. The application of pressure tuning is predicted to transform the topological characteristics of P4/nmm-TaSb, causing it to transition from a topological insulator state to a Dirac semimetal state and ultimately reverting back to a topological insulator state. Therefore, the P4/nmm-TaSb compound is considered a promising candidate to investigate topological and superconducting excitations. Moreover, the mechanical and thermal properties of Ta–Sb binary phases were also investigated. The thermal conductivity of I4/mmm-TaSb2, P4/nmm-TaSb, and P4/nmm-TaSb3 all surpasses 20 W m−1 K−1 at 1000 K, showcasing their excellent thermal conductivity properties. The present study addresses the research gap concerning high-pressure structures in the Ta–Sb binary system, thereby offering valuable insights for the design and development of intermetallic compounds within this binary system. [ABSTRACT FROM AUTHOR]

We have grown and characterized (110)-oriented YBa2Cu3O7−x (YBCO)/PrBa2(Cu0.8Ga0.2)3O7−x (PBCGO) bilayer and YBCO/PBCGO/YBCO trilayer heterostructures, which were deposited by pulsed laser deposition technique for the nanofabrication of (110)-oriented YBCO-based superconductor (S)/insulator (I)/superconductor (S) tunneling vertical geometry Josephson junction and other superconductor electronic devices. The structural properties of these heterostructures, investigated through various x-ray diffraction techniques (profile, x-ray reflectivity, pole figure, and reciprocal mapping), showed (110)-oriented epitaxial growth with a preferred c-axis-in-plane direction for all layers of the heterostructures. The atomic force microscopy measurement on the top surface of the heterostructures showed crack-free and pinhole-free, compact surface morphology with about a few nanometer root mean square roughness over the 5 × 5 μm2 region. The electrical resistivity measurements on the (110)-direction of the heterostructures showed superconducting critical temperature (Tc) values above 77 K and a very small proximity effect due to the interfacial contact of the superconducting YBCO layers with the PBCGO insulating layer. Raman spectroscopy measurements on the heterostructures showed the softening of the Ag-type Raman modes associated with the apical oxygen O(4) and O(2)-O(3)-in-phase vibrations compared to the stand-alone (110)-oriented PBCGO due to the residual stress and additional two Raman modes at ∼600 and ∼285 cm−1 frequencies due to the disorder at the Cu–O chain site of the PBCGO. The growth process and structural, electrical transport, and Raman spectroscopy characterization of (110)-oriented YBCO/PBCGO bilayer and YBCO/PBCGO/YBCO trilayer heterostructures are discussed in detail. [ABSTRACT FROM AUTHOR]

The theory-led prediction of LaBeH8, which has a high superconducting critical temperature (Tc) above liquid nitrogen under a pressure level below 1 Mbar, has been experimentally confirmed. YBeH8, which has a structural configuration similar to that of LaBeH8, has also been predicted to be a high-temperature superconductor at high pressure. In this study, we focus on the structural phase transition and superconductivity of YBeH8 under pressure by using first-principles calculations. Except for the known face-centered cubic phase of Fm 3 ̄ m, we found a monoclinic phase with P 1 ̄ symmetry. Moreover, the P 1 ̄ phase transforms to the Fm 3 ̄ m phase at ∼200 GPa with zero-point energy corrections. Interestingly, the P 1 ̄ phase undergoes a complex electronic phase transition from semiconductor to metal and then to superconducting states with a low Tc of 40 K at 200 GPa. The Fm 3 ̄ m phase exhibits a high Tc of 201 K at 200 GPa, and its Tc does not change significantly with pressure. When we combine the method using two coupling constants, λopt and λac, with first-principles calculations, λopt is mainly supplied by the Be–H alloy backbone, which accounts for about 85% of total λ and makes the greatest contribution to the high Tc. These insights not only contribute to a deeper understanding of the superconducting behavior of this ternary hydride but may also guide the experimental synthesis of hydrogen-rich compounds. [ABSTRACT FROM AUTHOR]

To obtain high-performance THz-wave-emitting devices made of single crystals of Bi 2 Sr 2 CaCu 2 O 8 + δ (Bi2212), a high-temperature superconductor, an understanding of the device characteristics based on crystal characteristics can be a key issue because, in principle, the electrical properties of the intrinsic Josephson junctions (IJJs) constructed in Bi2212 crystals highly depend on crystal conditions, such as carrier concentration, crystal homogeneities, and crystal defects. To evaluate the tendencies of the device characteristics associated with crystal characteristics, we prepared Bi2212 crystals with different Bi/Sr ratios (x = 0.05 , 0.15, and 0.25) and δ values (annealed under N 2 or O 2 gas flow conditions). The unit cell parameter c decreased as the Bi/Sr ratio or δ increased. For the same annealing conditions under N 2 gas flow, the superconducting transition temperature as well as the size of the hysteresis loop of the current–voltage characteristics and emission characteristics were significantly suppressed for the sample with x = 0.25 compared with the corresponding values for the samples with x = 0.05 and 0.15. The experimental results clearly indicate that parameters, such as the Bi/Sr ratio and annealing conditions, are crucial factors in determining the electrical characteristics of a device. This information can be a useful guide for the preparation of crystals for IJJ THz-wave devices that can be fine-tuned according to the desired device characteristics. [ABSTRACT FROM AUTHOR]

Nickel/bismuth (Ni/Bi) bilayers have recently attracted attention due to the occurrence of time-reversal symmetry breaking in the superconducting state. Here, we report on the structural, magnetic, and electric characterization of thin film Ni/Bi bilayers with several Bi thicknesses. We observed the formation of a complex layered structure depending on the Bi thickness caused by the inter-diffusion of Bi and Ni which leads to the stabilization of NiBi 3 at the Bi/Ni interface. The superconducting transition temperature and the transition width are highly dependent on the Bi thickness and the layer structure. Magnetoelectric transport measurements in perpendicular and parallel magnetic fields were used to investigate the temperature-dependent upper critical field within the framework of the anisotropic Ginzburg–Landau theory and the Werthamer–Helfand–Hohenberg model. For thicker samples, we observed a conventional behavior, similar to that shown by NiBi 3 bulk samples, including a small Maki parameter (α M = 0), no spin–orbit scattering (λ S O = 0) and nearly isotropic coherence length (γ = ξ ⊥ (0) / ξ ∥ (0) ≈ 1). The values obtained for these properties are close to those characterizing NiBi 3 single crystals. On the other hand, in very thin samples, the Maki parameter increases to about α M = 2.8. In addition, the coherence length becomes anisotropic (γ = 0.32) and spin–orbit scattering (λ S O = 1.2) must be taken into account. Our results unequivocally show that the properties characterizing the superconducting state in the Ni/Bi are strongly dependent on the sample thickness. [ABSTRACT FROM AUTHOR]

We have investigated the effect of gamma (γ)-irradiation on the structural and superconducting properties of FeTe0.55Se0.45 single crystals grown by the self-flux method. The impact of γ-irradiation on the superconducting transition temperature (TC), critical current density (JC), and vortex pinning mechanism has been systematically studied. The x-ray diffraction study reveals the growth of single crystals along the c-axis. The superconductivity has been confirmed in pristine and γ-irradiated samples through temperature-dependent resistivity (ρ (T)) and magnetization [M(T)] measurements. After irradiation, a slight improvement is observed in the upper critical field H c 2 (0) values. The values of thermally activated energy have been calculated and a crossover from a single to collective vortex pinning regime is observed. Additionally, we have analyzed the vortex phase diagrams, revealing a transition from vortex liquid to vortex glass state. Furthermore, the presence of second magnetization peak (SMP) or fishtail effect has been noticed in the M(H) loops, and with increasing temperature, the position of SMP (H s p ) shifts toward lower magnetic field regions. The critical current density has been estimated by Bean's critical state model at different magnetic fields [JC(H)] and temperatures [JC(T)]. The defects through gamma-irradiation lead to a significant threefold increase in JC compared to pristine samples in self-field and at 2 K. The pinning mechanisms have been explained using collective pinning theory and the Dew-Hughes model by analyzing the normalized pinning force density. Our analysis indicates that δl-pinning is dominant and point defects are present in all the samples. [ABSTRACT FROM AUTHOR]

Sr2CoRuO6 in its bulk form shows spin glass behavior with a transition temperature of 95 K, and in its epitaxial thin film, it shows similar behavior with a transition temperature of 135 K. We have studied the structural, electronic, and magnetic properties of a polycrystalline thin film of oxygen-deficient Sr2CoRuO6−δ (SCRO), which shows ferrimagnetic or glassy behavior up to room temperature. The presence of oxygen deficiency causes multivalent cations Co3+ and Co2+ and Ru4+ and Ru5+, which introduces various kinds of magnetic interactions between Co3+–O–Co2+, Co3+–O–Ru4+, Co2+–O–Ru4+, Co3+–O–Ru5+, and Co2+–O–Ru5+ exchange paths, producing unusual exchange bias effects in the single layer thin film of SCRO. The interionic charge transfer between Co and Ru ions as a result of the negative charge transfer energy of the system helps in visualizing the unconventional exchange bias effect in the system. [ABSTRACT FROM AUTHOR]

Despite widespread interest in the phase-change applications of vanadium dioxide (VO2), the fabrication of high-quality VO2 thin films with elevated transition temperatures (TIMT) and high insulator–metal-transition resistance switching still remains a challenge. This study introduces a two-step atmospheric oxidation approach to fabricate bilayer VO2−x/VO2 films on a c-plane sapphire substrate. To quantify the impact of the VO2 buffer layer, a single-layer VO2 film of the same thickness was also fabricated. The bilayer VO2−x/VO2 films, wherein the top VO2−x film was under-oxidized, demonstrated an elevation in TIMT reaching ∼97 °C, one of the highest reported to date for VO2 films and is achieved in a doping-free manner. Our results also reveal a one-order increase in resistance switching, with the optimum bilayer VO2/VO2 film exhibiting ∼3.6 orders of switching from 25 to 110 °C, compared to the optimum single-layer VO2 reference film. This is accompanied by a one-order decrease in the on-state resistance in its metallic phase. The elevation in TIMT, coupled with increased strain extracted from the XRD characterization of the bilayer film, suggests the possibility of compressive strain along the c-axis. These VO2−x/VO2 films also demonstrate a significant change in the slope of their resistance vs temperature curves contrary to the conventional smooth transition. This feature was ascribed to the rutile/monoclinic quasi-heterostructure formed due to the top VO2−x film having a reduced TIMT. Our findings carry significant implications for both the lucid fabrication of VO2 thin film devices as well as the study of phase transitions in correlated oxides. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2) is a highly attractive and multifunctional material for technological applications due to its metal–insulator transition, which is accompanied by several orders of magnitude changes in electrical resistivity and optical transmissivity. In this work, we report on the metal–insulator transition of VO2 nanoparticles which are produced by a simple, efficient, and low-cost two-step preparation method based on infrared laser irradiation of V2O5 powder dispersed in water and subsequent stoichiometric stabilization by vacuum annealing at 773 K. VO2 nanoparticles have an average size of 36 nm with facet-like contours and undergo a structural phase transition from a monoclinic to a tetragonal phase, accompanied by a metal–insulator transition occurring around 323 K, which is about 17 K lower than bulk VO2. No evidence of the formation of intermediary metastable phases is observed. Our findings reveal that the size of VO2 nanoparticles is a key parameter to moving the transition closer to room temperature, which is important for many applications. [ABSTRACT FROM AUTHOR]

Next-generation superconducting radio frequency (SRF) cavities, based on tailored thin films, would allow for more efficient and sustainable accelerators operating at higher accelerating gradients. In particular, superconductor–insulator–superconductor (SIS) multilayers are proposed as a potential alternative to bulk Nb. In this context, NbTiN stands out as a superconducting candidate. Here, we report our studies on NbTiN thin films grown by plasma-enhanced atomic layer deposition (PEALD) in a supercycle approach on AlN in situ deposited on planar silicon substrates. In detail, different ternary compound compositions and thicknesses have been investigated concerning the elemental composition, the superconducting properties, and the crystallinity of the deposited thin films. Two different post-deposition thermal treatments have been applied to Nb0.75Ti0.25N thin films of different thicknesses. Their effect on the film properties has been evaluated. It has been demonstrated that an optimized post-deposition thermal annealing procedure significantly improves the quality of our PEALD deposited Nb0.75Ti0.25N thin films, achieving the highest superconducting critical temperature (Tc) of 15.9 K obtained for films deposited by atomic layer deposition (ALD) so far and a lower critical field (Hc1) of 213 mT, which overpasses the bulk Nb intrinsic limit of 200 mT. Our studies are a promising first stepping stone on the path toward tailored thin films based SRF cavities. [ABSTRACT FROM AUTHOR]

Electron–phonon (e–ph) interaction plays a crucial role in determining many physical properties of the materials, such as the superconducting transition temperature, the relaxation time and mean free path of hot carriers, the temperature dependence of the electronic structure, and the formation of the vibrational polaritons. In the past two decades, the calculations of e–ph properties from first-principles has become possible. In particular, the renormalization of electronic structures due to e–ph interaction can be evaluated, providing greater insight into the quantum zero-point motion effect and the temperature dependence behavior. In this perspective, we briefly overview the basic theory, outline the computational challenges, and describe the recent progress in this field, as well as future directions and opportunities of the e–ph coupling calculations. [ABSTRACT FROM AUTHOR]

Dirac materials, due to their unique physical properties, hold vast prospects in both fundamental research and practical applications. Recently, the metallic Dirac material, molybdenene, has been synthesized. However, free-standing molybdenene is found to be dynamically unstable. We propose the use of F/Li to modify its structure and stabilize it. Based on density functional theory, density functional perturbation theory, and anisotropic Migdal–Eliashberg equations, we systematically investigate the electronic structures and superconducting properties of MoF and MoLi. The results indicate that both MoF and MoLi are intrinsic superconductors, with electron–phonon coupling constants of 0.49 and 0.74, respectively. Solving the superconducting gap equation yields a superconducting transition temperature of 7.5 K for MoLi. Further analysis suggests that the coupling between the out-of-plane component of Mo's d orbital electrons and the vibrations of Mo atoms contributes significantly to the electron–phonon coupling in MoLi. Our study lays the foundation for further applications of molybdenene. [ABSTRACT FROM AUTHOR]

SrTiO3-based conducting interfaces, which exhibit coexistence of gate-tunable 2D superconductivity and strong Rashba spin-orbit coupling (RSOC), are candidates to host topological superconductive phases. Yet, superconductivity is usually in the dirty limit, which tends to suppress nonconventional pairing and therefore challenges these expectations. Here we report on LaAlO3/SrTiO3 (LAO/STO) interfaces with large mobility and mean free paths comparable to the superconducting coherence length, approaching the clean limit for superconductivity. We further show that the carrier density, mobility, and formation of the superconducting condensate are controlled by the fine-tuning of La/Al chemical ratio in the LAO film. We find a region in the superconducting phase diagram where the critical temperature is not suppressed below the Lifshitz transition, at odds with previous experimental investigations. These findings point out the relevance of achieving a clean-limit regime to enhance the observation of unconventional pairing mechanisms in these systems. SrTiO3-based oxide interfaces, which exhibit coexistence of gate-tunable two-dimensional superconductivity and Rashba spin-orbit coupling, are candidates to host topological superconductive phases. By controlling the chemical ratio in LaAlO3, the authors demonstrate tuning of carrier densities, mobilities and the formation of superconductivity, showing that, approaching to clean limit, significant enhancement below the Lifshitz transition is observed, at odds with previous experimental investigations. [ABSTRACT FROM AUTHOR]

Phonon anharmonicity plays a crucial role in determining the stability and vibrational properties of high-pressure hydrides. Furthermore, strong anharmonicity can render phonon quasiparticle picture obsolete questioning standard approaches for modeling superconductivity in these material systems. In this work, we show the effects of non-Lorentzian phonon lineshapes on the superconductivity of high-pressure solid hydrogen. We calculate the superconducting critical temperature TC ab initio considering the full phonon spectral function and show that it overall enhances the TC estimate. The anharmonicity-induced phonon softening exhibited in spectral functions increases the estimate of the critical temperature, while the broadening of phonon lines due to phonon-phonon interaction decreases it. Our calculations also reveal that superconductivity emerges in hydrogen in the Cmca − 12 molecular phase VI at pressures between 450 and 500 GPa and explain the disagreement between the previous theoretical results and experiments. This work studies the effects of non-gaussian phonon lineshapes from stochastic self-consistent harmonic approximation on the superconducting critical temperature (Tc) of hydrogen at high pressure. It predicts superconductivity in the Cmca-12 phase between 450 and 500 GPa and an increase in Tc for both the Cmca-12 and the I41/amd-2 structures compared to harmonic calculations. [ABSTRACT FROM AUTHOR]

High‐entropy materials, an exciting new class of structural materials involving five or more elements, are emerging as unexplored ground for superconductors. Here, the effects of nitrogen stoichiometry are investigated on local chemical structure of TiZrNbTa‐based thin films by various X‐ray‐based techniques. Lattice distortion and short‐range order of a set of TiZrNbTaNx samples, including bond lengths of different atomic pairs and coordination numbers of substituting atoms are quantitatively studied. The maximum superconducting transition temperature Tc is found at 10 K for a near‐stoichiometric (TiZrNbTa)N1.08 film, which is >8 K measured for a metallic TiZrNbTa film. The underlying electronic structure and chemical bonding in these high entropy nitrides thus influence the superconducting macroscopic properties. [ABSTRACT FROM AUTHOR]

A recent experiment [Nakajima, et al., Nature 613, 479 (2023)] has reported a pair of oppositely polarized spins under an alternating electric current in a superconductor with a chiral structure. However, these behaviors cannot be explained by the conventional Edelstein effect and require a new mechanism. In this Letter, we propose a mechanism of spin current generation under an external electric field due to chiral phonons in a chiral-structure superconductor based on the Bogoliubov de Gennes and the Boltzmann equations. In our mechanism, chiral phonons are induced by electric field due to inversion symmetry breaking and electron–phonon interaction. They work as an effective Zeeman field and hence spin-polarize Bogoliubov quasiparticles in the superconductor. As a result, the spin current carried by the quasiparticles flows along the screw axis and shows a quadratic dependence on the electric field at the low-field range, leading to a nonreciprocal spin transport. The spin current also shows a nonmonotonic temperature dependence, reaching its maximum at around the superconducting transition temperature. [ABSTRACT FROM AUTHOR]

In a superconductor/ferromagnet hybrid, a magnetically controlled singlet-to-triplet Cooper pair conversion can modulate the superconducting critical temperature. In these triplet superconducting spin valves, such control usually requires inhomogeneous magnetism. However, in the presence of spin–orbit coupling from an interfacial heavy metal layer, the singlet/triplet conversion rate and, thus, critical temperature can be controlled via the magnetization direction of a single homogeneous ferromagnet. Here, we report significantly enhanced controllable pair conversion to a triplet state in a Nb/Pt/Co/Pt superconducting spin valve in which Pt/Co/Pt is homogenously magnetized and proximity-coupled to a superconducting layer of Nb. The Co/Pt interface furthest away from Nb is modified by a sub-nanometer-thick layer of Cu or Au. We argue that the enhancement is most likely associated from an improvement of the Co/Pt interface due to the insertion of Cu and Au layers. Additionally, the higher normalized orbital moments in Au measured using x-ray magnetic circular dichroism shows that increasing spin–orbit coupling enhances the triplet proximity effect—an observation supported by our theoretical calculations. Our results provide a pathway to enhancing triplet pair creation by interface engineering for device development in superspintronics. [ABSTRACT FROM AUTHOR]

We explored superconductors with high superconducting transition temperatures (Tc) tuning the stability of Magnéli phase through high-pressure torsion (HPT). This study has started from exploring superconducting states in the Al–Mg–O ternary system along with the prediction using machine learning. We successfully found superconducting states with Tc = 4.0 and 7.3 K for a composition of Al:Ti = 1:2 in the mixture of Al and surface-oxidized Ti powders. Another magnetic anomaly was also observed at ~ 93 K, being supported by the Tc prediction using the machine learning for the Al–Ti–O system. In this study, the HPT processing was also performed on a Magnéli material Ti4O7 and such mixtures of stable materials as Al + TiO2, Al2O3 + Ti, Al2O3 + TiO2, and Al + Ti4O7. In HPT-processed Ti4O7, the metal–insulator transition was maintained even after the HPT processing. HPT experiments using stable oxides indicate the difficulty of newly stabilizing the Magnéli phase starting from thermodynamically stable materials under severe plastic deformation. A series of attempts reveals that the superconducting state in the mixture with ratio Al:Ti = 1:2 is attributed to both strained Ti-oxide created on the surface of the Ti powder and its reaction with Al under HPT processing, resulting in the stabilization of a Magnéli phase. [ABSTRACT FROM AUTHOR]

Hydrogen-based compounds have been found to exhibit high superconducting critical temperature ( T c ) through the electron–phonon coupling mechanism under ultrahigh pressure. Herein, a new two-dimensional transition metal dichalcogenide material is constructed, namely, the Janus WSH monolayer. It is formed by replacing one layer of S atoms in the WS2 monolayer with H atoms. Then the electronic structure, phonon dispersion, electron–phonon coupling, and superconductivity are investigated by first-principles calculations. The results show that the introduction of H atoms helps to flatten the electronic dispersion and leads to high electronic density of states at the Fermi level, resulting in strong electron–phonon coupling. Additionally, the softening of phonon modes from the hybridization of in-plane W atomic vibrations and out-of-plane H atomic vibrations boosts the electron–phonon coupling further. The strong interactions between electrons and phonons lead to phonon-mediated superconductivity in Janus WSH monolayer with a calculated T c being about 23.1 K. This is the highest T c predicted in WS2-based materials at present, which indicates that hydrogenation is a great way to improve the T c of transition metal dichalcogenide materials. [ABSTRACT FROM AUTHOR]

The evolution of the temperature dependence of the pseudogap Δ*(T) in optimally doped (OD) YBa2Cu3O7–δ (YBCO) films with the superconducting critical temperature Tc = 88.7 K under the influence of a magnetic field B has been studied in detail. It has been established that the shape of Δ*(T) for various B over the entire range from the pseudogap opening temperature T* to T01, below which superconducting fluctuations occur, has a wide maximum at the BEC-BCS crossover temperature Tpair, which is typical for OD films and untwinned YBCO single crystals. T* was shown to be independent on B, whereas Tpair shifts to the low-temperature region along with the increase in B, while the maximum value of Δ*(Tpair) remains practically constant regardless of B. It was revealed that as the field increases, the low-temperature maximum near the 3D-2D transition temperature T0 is blurred and disappears at B > 5 T. Moreover, above the Ginzburg temperature TG, which limits superconducting fluctuations from below, for B > 0.5 T, a minimum appears on Δ*(T) at Tmin, which becomes very pronounced with a further increase in B. As a result, the overall value of Δ*(T) decreases noticeably most likely due to the pair-breaking effect. A comparison of Δ*(T) near Tc with the Peters–Bauer theory shows that the density of fluctuating Cooper pairs actually decreases from ⟨n↑n↓⟩ ≈ 0.31 at B = 0 to ⟨n↑n↓⟩ ≈ 0.28 in the field of 8 T. The observed behavior of Δ*(T) around Tmin is assumed to be due to the influence of a two-dimensional vortex lattice created by the magnetic field, which prevents the formation of fluctuating Cooper pairs near Tc. [ABSTRACT FROM AUTHOR]

For X-ray applications, microcalorimeters are increasingly dependent on the superconducting transition-edge sensor (TES) technology. We are developing TES devices based on Mo–Cu bilayer films for the proposed Hot Universe Baryon Surveyor (HUBS) satellite mission. To investigate the possible impact of a space radiation environment on the stability of the bilayer films, we conducted an irradiation experiment on Mo–Cu bilayer samples with 1 MeV protons at room temperatures and liquid nitrogen temperatures. With data recorded in real time, we noticed that the changes in the electrical resistance of the film samples were not apparent during irradiation at room temperatures, before and after irradiation, but were evident at liquid nitrogen temperatures. Furthermore, following the irradiation runs, we warmed up the irradiated film samples and placed them in a refrigerator to measure their superconducting transition temperatures ( T c ) and residual resistivity ( ρ 3 K ). We found no systematic change in T c and ρ 3 K . We discuss the results in terms of the vacancies and interstitials in the test samples that are produced by irradiation, as well as the effects of heating caused by irradiation. [ABSTRACT FROM AUTHOR]

We have studied THz heterodyne detection in sub-micrometer MgB2 hot electron bolometer (HEB) mixers based on superconducting MgB2 films of ∼ 5 nm (HEB-A), corresponding to a critical temperature (Tc) of 33.9 K, and ∼ 7 nm (HEB-B), corresponding to a T c of 38.4 K. We have measured a double sideband (DSB) receiver noise temperature of 2590 K for HEB-A and 2160 K for HEB-B at 1.6 THz and 5 K. By correcting for optical losses, both HEBs show receiver noise temperatures of ∼1600 K referenced to the front of anti-reflection (AR)-coated Si lenses. An intermediate frequency (IF) noise bandwidth of 11 GHz has been measured for both devices. The required local oscillator (LO) power is about 13 μW for both HEBs. We have also measured a DSB receiver noise temperature of 3290 K at 2.5 THz and 5 K but with an AR-coated lens optimized for 1.6 THz. Besides, we have observed a step-like structure in current voltage (IV) curves, which becomes weaker when the LO power increases and observable only in their differential resistance. Such a correlated structure appears also in the receiver output power as a function of voltage, which is likely due to electronic inhomogeneities intrinsic to the variations in the thickness of the MgB2 films. Different behavior in the IV curves around the low bias voltages, pumped with the same LO power at 1.6 and 5.3 THz, was observed for HEB-B, suggesting the presence of a high-energy σ-gap in the MgB2 film. [ABSTRACT FROM AUTHOR]

VO2 thin films are fabricated by the reactive high power impulse magnetron sputtering technique. Their thermochromic properties are found to be greatly affected by the addition of nitrogen during the deposition process. These include an effect of localized surface plasmon resonance due to isolated island structures. Furthermore, low transition temperatures below 45 °C are observed due to oxygen-deficient conditions. Also, the transition temperature decreases with an increase in the thickness of the TiO2 buffer layer. The reduction in transition temperature could be as low as 39 °C with a solar modulating ability of 4% at a thicker buffer of 300 nm under a high gas ratio of 21.7% for nitrogen. The crystalline phase is identified by x-ray diffraction, showing that the intensity of monoclinic crystallites at a diffraction angle of 2θ = 27.8° for (011) phase decreases with an increase in the amount of nitrogen, whereas a relaxing shift is detected near the diffraction angle of 2θ = 37.0° for ( 2 ¯ 11) phase. Similar behavior is seen in the peak shift of the (004) phase for TiO2. The d-spacing of the crystallization phase with island structure is identified by high-resolution transmission electron microscopy. The evolution of stress release, which is strongly dependent on surface morphology, is consistent with x-ray pole figure representation. The visible transmittance and solar modulation ability as functions of the amount of nitrogen and the buffer thickness of TiO2 are discussed. [ABSTRACT FROM AUTHOR]

We present an analytically solvable theory of Bardeen-Cooper-Schrieffer-type superconductivity in good metals which are confined along one of the three spatial directions, such as thin films. Closed-form expressions for the dependence of the superconducting critical temperature T c as a function of the confinement size L are obtained, in quantitative agreement with experimental data with no adjustable parameters. Upon increasing the confinement, a crossover from a spherical Fermi surface, which contains two growing hollow spheres corresponding to states forbidden by confinement, to a strongly deformed Fermi surface, is predicted. This crossover represents a new topological transition, driven by confinement, between two Fermi surfaces belonging to two different homotopy classes. This topological transition provides a mechanistic explanation of the commonly observed non-monotonic dependence of T c upon film thickness with a maximum which, according to our theory, coincides with the topological transition. [ABSTRACT FROM AUTHOR]

To date, superconductivity in fullerides has been almost exclusively tuned by (chemical or physical) pressure control of the conduction bandwidth, W at half filling. This contrasts sharply with the extensive control of the superconducting transition temperature, T c in atom-based superconductors such as the cuprates and iron pnictides and chalcogenides via changes in valence (bandfilling). Here, we investigate the effect of doping away from the exactly half-filled C 6 0 3 − level in quaternary face-centered-cubic (fcc) — structured fulleride solids with nominal composition ( Rb 2. 5 − x Csx) Ba 0. 5 C 6 0 (0 ≤ x ≤ 2. 5), in which divalent Ba 2 + ions partially replace monovalent alkali Rb + / Cs + ions. The resulting charged-modified fullerides in which the t 1 u bandwidth is also varied with changing x show a dome-shaped dependence of T c on interfullerene separation in analogy with their half-filled antecedents. However, following electron injection beyond half-filling, the superconductivity dome is found to shift towards shorter interfullerene separations, i.e. towards increased conduction bandwidths. [ABSTRACT FROM AUTHOR]

We show that the temperature-dependent superconducting order parameter and related superconducting properties (in particular, the temperature dependences of specific heat, superfluid density and related London penetration depth) of high- T c cuprates are fundamentally different from those of conventional superconductors and cannot be understood within the existing theories based on the Bardeen–Cooper–Schrieffer (BCS)-type condensation of weakly bound Cooper pairs into a superfluid Fermi-liquid and on the usual Bose–Einstein condensation (BEC) of bosonic Cooper pairs. We examine the validity of an alternative approach to the unconventional superconductivity in high- T c cuprates and establish that these materials exhibiting a λ -like superconducting transition at the critical temperature T c are similar to the superfluid 4He and are also superfluid Bose systems. We argue that the doped high- T c cuprates, from underdoped to overdoped regime, are unconventional (bosonic) superconductors and the tightly bound (polaronic) Cooper pairs in these polar materials behave like composite bosons just like 4He atoms and condense into a Bose superfluid at T c . We identify the superconducting order parameter Δ SC in underdoped and optimally doped cuprates as the coherence parameter Δ B of bosonic Cooper pairs, which appears just below T c and has a kink-like temperature dependence near the characteristic temperature T c ∗ < T c . We find that the λ -like specific heat anomaly in high- T c cuprates near T c predicted by the theory of Bose-liquid superconductivity is similar to that observed both in superfluid 4He near T λ and in Hg-based cuprate superconductor HgBa2Ca2Cu3O8 near T c ≃ 1 3 2 K. We demonstrate that in high- T c superconductor YBa2Cu3 O 6. 9 7 the superfluid density ρ s exhibits distinctly different temperature dependences in the temperature ranges 0 ≤ T ≤ T c ∗ and T c ∗ < T < T c . In this superconductor, a pronounced anomaly in ρ s (T) exists near T c ∗ ≃ 0. 4 T c and the temperature dependence of λ L 2 (0) / λ L 2 (T) below T c ∗ deviates downwards from the high-temperature behavior. Our results for the normalized superfluid density ρ s (T) / ρ s (0) = λ L 2 (0) / λ L 2 (T) are in good agreement with the experimental data on the temperature dependence of λ L 2 (0) / λ L 2 (T) in YBa2Cu3 O 6. 9 7 . The anomalous temperature dependences of specific heat and superfluid density observed in Hg- and Y-based high- T c superconductors are clear signatures of Bose-liquid superconductivity. [ABSTRACT FROM AUTHOR]

Since the prediction of multi‐hydrogen high‐temperature superconductor by Ashcroft in 2004, many possible candidates have been proposed, e.g., LaH10 showing the highest superconducting transition temperature (Tc) around 250–260 K at 170‐200 GPa hitherto. However, this pressure is too large to be taken into practical use. To address this challenge, it proposes a few‐hydrogen metal‐bonded perovskite superconductor, MgHCu3, by combining a novel design idea with first‐principles calculations. Different from multi‐hydrogen hydrides, whose high Tc relies on extreme pressure, the metallic bond in few‐hydrogen superconductor MgHCu3 improves the structural stability and ductility at atmospheric pressure. Here, the small amount of hydrogen is found to be vital for Tc. After the incorporation of hydrogen, the electron–phonon coupling constant of MgHCu3 is increased to 0.83, which is larger than that of the well‐known MgB2. Moreover, the anisotropy of MgHCu3 also plays an important role in enhancing Tc. Based on the Migdal‐Eliashberg theory, it predicts that the phonon‐mediated metal‐bonded perovskite MgHCu3 is a superconductor with Tc of 42 K. The first predicted ternary metal‐bonded perovskite, MgHCu3, enriches the family of perovskite and will promote further investigation on few‐hydrogen superconductors under atmospheric pressure. [ABSTRACT FROM AUTHOR]

We theoretically investigate the Seebeck and Peltier effect across an interacting quantum dot (QD) coupled between a normal metal and a Bardeen–Cooper–Schrieffer superconductor within the Coulomb blockade regime. Our results demonstrate that the thermoelectric conversion efficiency at optimal power output (optimized with respect to QD energy level and external serial load) in NQDS nanodevice can reach up to 58 % η C , where η C is Carnot efficiency, with output power P max ≈ 35 fW for temperature below the superconducting transition temperature. Further, the Peltier cooling effect is observed for a wide range of parameter regimes, which can be optimized by varying the background thermal energy, QD level energy, QD-reservoir tunneling strength, and bias voltage. The results presented in this study are within the scope of existing experimental capabilities for designing miniature hybrid devices that operate at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Superconductivity enhancement is often associated with phonon softening by doping or external pressure. In this paper, we report L 1 2 -type trialuminides Al3V as a typical example belonging to this scenario. The electronic, phononic and superconducting properties have been studied by using the first-principle method. Under uniaxial compression, the superconducting transition temperature Tc of Al3V can be increased from ≈1.5 K to its maximum at ≈7.3 K when the lattice approaches the structural instability. A detailed investigation of Al3V reveals that the (V: d)-(Al: p) hybrid bands are strongly coupled to the phonon modes with lower frequency. The uniaxial compression induces a significant softening of the phonon mode with non-zero phonon line-width, and yet keeps the electron density of states near the Fermi level unchanged. This leads to a stronger electron–phonon coupling (EPC) and therefore a higher Tc. On the contrary, the L 1 2 structure is more stable against the hydrostatic pressure and the phonon energy actually grows up when the hydrostatic pressure is increased. As a result, EPC becomes weaker and Tc can be reduced to ⩽ 0.3 K under high hydrostatic pressure. Our results present an interesting example that superconductivity can enhanced by tuning the softened phonon via pressure or doping. [ABSTRACT FROM AUTHOR]

The superconducting properties of a Co/Pb/Co heterostructure with thin insulating spacers, which are oxidized superconductor/ferromagnet interfaces, have been studied. The behavior of the critical transition temperature Tc of the heterostructure to a superconducting state at a change in the relative orientation of the magnetizations of the ferromagnetic layers from antiparallel to parallel (the so-called superconducting spin valve effect) has been examined. This effect is usually most pronounced in the case of a perfect metal contact at superconductor/ferromagnet interfaces. In this work, a significant superconducting spin valve effect is observed in structures with worsened superconductor/ferromagnet interfaces. A change in the relative orientation of the magnetizations of two ferromagnetic Co layers from antiparallel to parallel leads to the change in Tc by 0.2 K at the optimal thickness of the superconducting Pb layer. Our studies verify the still unconfirmed results obtained in [G. Deutscher and F. Meunier, Phys. Rev. Lett. 22, 395 (1969)] and open new interesting possibilities for improving the parameters of the superconducting spin valve. [ABSTRACT FROM AUTHOR]

The combination of strongly coupled Cooper pairs and weak superconducting fluctuations is an important prerequisite for achieving high-temperature superconductivity. The review is devoted to the implementation of this condition in multiband superconductors, in which strongly coupled pairs in the shallow conduction band (the Fermi level is close to the band edge) coexist with ordinary, weakly fluctuating Cooper pairs formed in the deep band. As a result of the Josephson coupling between condensates in different bands, such a system is characterized by a high critical coherence temperature due to the presence of strongly coupled pairs and the suppression of superconducting fluctuations. This suppression does not require any special preconditions, and is almost total even if the Josephson coupling between the bands is weak. [ABSTRACT FROM AUTHOR]

Herein, the preparation process, morphology, structure, and magnetic properties of La1.85Sr0.15CuO4 (LSCO) cobweb-like nanofibers are reported. LSCO nanofibers with a regular grain size distribution are successfully prepared via electrospinning, followed by calcination. We conducted morphology analysis and elemental distribution using electron microscopy and energy-dispersive X-ray spectroscopy (EDS), respectively. Additionally, magnetic property testing was performed using a vibrating sample magnetometer (VSM) to confirm the superconducting properties of the samples. Interestingly, our samples exhibited a superconducting transition temperature, Tc, of 25.21 K, which showed some disparity compared to similar works. Furthermore, we observed a ferromagnetic response at low temperatures in the superconducting nanofibers. We attribute these phenomena to the effects generated by surface states of nanoscale superconducting materials. [ABSTRACT FROM AUTHOR]

A comprehensive study of magnetotransport and field‐dependent specific heat of FeTe0.58Se0.42 single crystals synthesized using the self‐flux method is reported. The transport measurement reveals the presence of Fermi liquid behavior in the normal state resistivity of the single crystals. Furthermore, the grown single crystals exhibit anisotropy and demonstrate a high value of upper critical magnetic field (HC2). The magnetoresistance exhibits a linear behavior as the magnetic field increases, suggesting the possible presence of a Dirac‐cone state. Anisotropy is also observed in magnetoresistance near the superconducting transition temperature (TC). The sign reversal of the Hall coefficient and the violation of Kohler's rules are observed, which provide evidence of the presence of multiband effects in FeTe0.58Se0.42 single crystals. Specific heat measurements confirm the bulk superconductivity in the grown single crystals. Additionally, the specific heat jump ΔC(TC)/TC is estimated, which is approximately equal to 26 mJ mol−1 K−2. The magnetic field‐dependent specific heat also suggests multiband superconductivity and offers insights into the upper critical field. Furthermore, the electronic specific heat (Cel) is best fitted with a two‐band model. Moreover, the field‐dependent residual Sommerfeld coefficient γ(H) gives information about the superconducting pairing symmetry. [ABSTRACT FROM AUTHOR]

The Simons Observatory (SO) is a cosmic microwave background instrumentation suite being deployed in the Atacama Desert in northern Chile. The telescopes within SO use three types of dichroic transition-edge sensor (TES) detector arrays, with the 90 and 150 GHz Mid-Frequency (MF) arrays containing 65% of the approximately 68,000 detectors in the first phase of SO. All of the 26 required MF detector arrays have now been fabricated, packaged into detector modules, and tested in laboratory cryostats. Across all modules, we find an average operable detector yield of 84% and median saturation powers of (2.8, 8.0) pW with interquartile ranges of (1, 2) pW at (90, 150) GHz, respectively, falling within their targeted ranges. We measure TES normal resistances and superconducting transition temperatures on each detector wafer to be uniform within 3%, with overall central values of 7.5 m Ω and 165 mK, respectively. Results on time constants, optical efficiency, and noise performance are also presented and are consistent with achieving instrument sensitivity forecasts. [ABSTRACT FROM AUTHOR]

Superconducting transition-edge sensors (TESs) are widely used to detect electromagnetic radiation ranging from millimeter wave to γ-ray photons. The energy resolution of TESs is mainly determined by their critical temperature (TC). We propose to tune the TC of Ti film by baking in air for a period at a moderate temperature and find that TC is inversely proportional to the logarithm of baking time (tbaking) for a given baking temperature (Tbaking), but scales with the square of Tbaking for a given tbaking. Ti film covered by a thin Au protection layer follows the same trend when baked in air. Based on the XPS analysis, we attribute the change in TC of Ti films to the oxidation at the surface and diffusion of oxygen into the films. In addition, the aging effect of Ti films is similar to that of baking in air but with much slower change rate. [ABSTRACT FROM AUTHOR]

The effect of samarium and lanthanum fluorides (SmF3 and LaF3) on the structural and superconducting properties of Tl0.8Hg0.2Ba2Ca2−xRxCu3O9-δ-yFy superconducting phase (Tl, Hg)-1223, where R = Sm or La and x = 0.00, 0.025, 0.050, 0.075, and 0.10 was investigated. The solid-state reaction method was used to synthesize the superconducting samples. The phase formation percentages and lattice parameters were calculated using X-ray powder diffraction (XRD). Images taken with a scanning electron microscope (SEM) show that the presence of both Sm and La increases the grain size and inter-grain connectivity up to x=0.025. The successful substitution of Sm and La elements in the crystal structure of (Tl, Hg)-1223 is confirmed by energy-dispersive X-ray (EDX) analysis. The oxidation states of the elements in the prepared samples are revealed by X-ray photoelectron spectroscopy (XPS) spectra. I–V and resistivity measurements were used to investigate the electrical properties of the (Tl, Hg)-1223 system with Sm and La substitutions. The superconducting transition temperature (Tc) and transport critical current density (Jc) have steadily improved up to x = 0.025, above which they dropped significantly. Furthermore, as temperature increased, the temperature dependence of fluctuation conductivity (Δσ), revealed distinct zones. The zero-temperature coherence length (ξc(0)), effective layer thickness of the two-dimensional system (d), interlayer coupling (I), Fermi velocity (vf), and Fermi energy (Ef) were determined. ξc(0) and d decrease until x= 0.025, then increase as x increases. All estimated I values show weak coupling between CuO2 planes and a transition from three-dimensional (3D) to two-dimensional (2D) regions. [ABSTRACT FROM AUTHOR]

Mn5Sn3−xInx (x = 0.1 and 0.25) alloys have been prepared and named as sample-1 and sample-2, respectively. Partial substitution of indium (In) and heat treatment conditions adopted have caused the alloys to crystallize with indium-containing-Mn2−ySn phase and MnSn2 phase. The magnetism in these alloys stem only from Mn2−ySn. This phase has two Mn sites such that its magnetic structure and doping-induced disorderliness cause frustration and randomness resulting in reentrant spin glass transition in the alloys. Indium-doping has induced superconductivity in these samples, which is novel to occur in Mn5Sn3 systems. The upper critical fields of the two alloys are as low as 3.11 and 4.11 kOe and the superconducting transition temperatures are 5.6 and 5.9 K, respectively. Besides, long-range ordering of moments in two Mn sites of Mn2−ySn phase has led to two separate transitions, and on the whole, the alloys are found to have complex magnetic ground state. The magnetocaloric properties are moderate, but indium-doping has increased the relative cooling power of these samples when compared to other Mn5Sn3 systems. [ABSTRACT FROM AUTHOR]

The non-toxic copper oxide superconductor, (Cu,C)Ba2Ca3Cu4O11+δ or (Cu,C)-1234, exhibits the highest irreversibility magnetic field among superconducting materials in the liquid nitrogen temperature range and can achieve a superconducting transition temperature of 117 K, providing a new sample system for physical studies of copper oxide high-temperature superconductors. This article examines the underlying mechanisms that contribute to the high critical transition temperature, high critical current density, and notable irreversibility field properties observed in superconductors based on (Cu,C)-1234 copper. It also investigates the recent advancements made in the methods employed for the fabrication of bulks and thin films of this superconductor. Additionally, a comparison is made between the performance parameters of (Cu,C)-1234 superconductors and other superconducting materials that possess critical temperatures surpassing 100 K. This comparison highlights the distinctive characteristics and advantages of (Cu,C)-1234. Finally, we present potential future applications in the fields of energy transmission, magnetic levitation, and scientific research. [ABSTRACT FROM AUTHOR]

The interplay between superconductivity and magnetism has been a subject of significant interest for decades. While extensive research has focused on modifying the superconducting state through a magnetic domain as an independent variable, the manipulation of magnetic domains by the superconducting state has been relatively unexplored, primarily due to their higher stiffness compared to the energy associated with superconducting vortices. In this Letter, we demonstrate the manipulation of magnetic domains by thermally activated superconducting vortices in a ferromagnet/superconductor hybrid. We observe a reversible domain transition between metastable magnetic stripes and bubbles in a Nb/CeRu2Ga2B hybrid induced by vortex motion and the trapped field within the Nb superconducting film. The comparable Curie and superconducting critical temperatures and the presence of magnetic metastable states enable the magnetic domain changes driven by superconducting vortices in this hybrid system. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) Dirac semimetal with concomitant superconductivity has been long sought but rarely reported. It is believed that light-element materials have the potential to realize this goal owing to their intrinsic lightweight and metallicity. Here, based on the recently synthesized β12 hydrogenated borophene, we investigate its counterpart named β12-B5H3. Our first-principles calculations suggest it has good stability. β12-B5H3 is a scarce Dirac semimetal demonstrating a strain-tunable phase transition from three Dirac cones to a single Dirac cone. Additionally, β12-B5H3 is also a superior phonon-mediated superconductor with a superconducting critical temperature of 32.4 K and can be further boosted to 42 K under external strain. The concurrence of Dirac fermions and superconductivity, supplemented with dual tunabilities, reveals β12-B5H3 is an attractive platform to study either quantum phase transition in 2D Dirac semimetal or the superconductivity or the exotic physics brought about by their interplay. The reduced dimensions of 2D materials increase the strength of electron-electron correlations and hence they can be used as a platform to engineer exotic physical states such as Dirac semimetals. Here, using first-principles calculations, the authors investigate the mechanical properties of β12-B5H3, as well as possible Dirac semimetal and phonon-mediated superconducting phases. [ABSTRACT FROM AUTHOR]

Pressure-induced superconductivity often occurs following structural transition under hydrostatic pressure (PHP) but disappears after the pressure is released. In the alkali-earth metal barium, superconductivity appears after structural transformation from body-centered cubic structure to hexagonal-close-packed (hcp) structure at PHP = 5 GPa, and the superconducting transition temperature (Tc) reaches a maximum of 5 K at PHP = 18 GPa. Furthermore, by stabilizing the low-temperature phase at PHP ~ 30 GPa, Tc reached a higher level of 8 K. Herein, we demonstrate a significantly higher Tc superconductivity in Ba even at ambient pressure. This was made possible through severe plastic deformation of high-pressure torsion (HPT). In this HPT-processed Ba, we observed superconductivity at Tc = 3 K and Tc = 24 K in the quasi-stabilized hcp and orthorhombic structures, respectively. In particular, the latter Tc represents the highest value achieved at ambient pressure among single-element superconducting metals, including intermetallics. The phenomenon is attributed to a strained high-pressure phase, stabilized by residual strains generated from lattice defects such as dislocations and grain boundaries. Significantly, the observed Tc far exceeds predictions from DFT calculations under normal hydrostatic compressions. The study demonstrates the importance of utilizing high-pressure strained phases as quasi-stable superconducting states at ambient pressure. [ABSTRACT FROM AUTHOR]

The ability to efficiently control charge and spin in the cuprate high-temperature superconductors is crucial for fundamental research and underpins technological development. Here, we explore the tunability of magnetism, superconductivity, and crystal structure in the stripe phase of the cuprate La2-xBaxCuO4, with x = 0.115 and 0.135, by employing temperature-dependent (down to 400 mK) muon-spin rotation and AC susceptibility, as well as X-ray scattering experiments under compressive uniaxial stress in the CuO2 plane. A sixfold increase of the three-dimensional (3D) superconducting critical temperature Tc and a full recovery of the 3D phase coherence is observed in both samples with the application of extremely low uniaxial stress of ~0.1 GPa. This finding demonstrates the removal of the well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the spin-stripe order temperature as well as the magnetic fraction at 400 mK show only a modest decrease under stress. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. However, strain produces an inhomogeneous suppression of the spin-stripe order at elevated temperatures. Namely, a substantial decrease of the magnetic volume fraction and a full suppression of the low-temperature tetragonal structure is found under stress, which is a necessary condition for the development of the 3D superconducting phase with optimal Tc. Our results evidence a remarkable cooperation between the long-range static spin-stripe order and the underlying crystalline order with the three-dimensional fully coherent superconductivity. Overall, these results suggest that the stripe- and the SC order may have a common physical mechanism. [ABSTRACT FROM AUTHOR]

As compressed hydrides constantly refresh the records of superconducting critical temperatures (Tc) in the vicinity of room temperature, this further reinforces the confidence to find more high-temperature superconducting hydrides. In this process, metastable phases of superhydrides offer enough possibilities to access superior superconducting properties. Here we report a metastable hexagonal lanthanum superhydride (P 63 /mmc -LaH10) stabilized at 146 GPa by introducing an appropriate proportion of Al, which exhibits high-temperature superconductivity with Tc ∼ 178 K, and this value is enhanced to a maximum Tc ∼ 223 K at 164 GPa. A huge upper critical magnetic field value Hc2(0) reaches 223 T at 146 GPa. The small volume expansion of P 63 /mmc -(La, Al) H10 compared with the binary LaH10 indicates the possible interstitial sites of Al atoms filling into the La–H lattice, instead of forming conventional ternary alloy-based superhydrides. This work provides a new strategy for metastable high-temperature superconductors through the multiple-element system. [ABSTRACT FROM AUTHOR]

In the present work, Tungsten trioxide (WO3) nanoparticles are added (up to 5 wt%) to Bi2Sr2.14Ca0.86Cu2Oy (Bi 2212) compound using a sol-casting method that facilitates their uniform distribution in the Bi 2212 matrix. Sintering at 870 oC, close to the melting point, has led to the formation of nearly spherical particles of WSr2CaO6 (W-alloy) phase (20–80 nm) by local reaction of distributed nano WO3 particles with Bi 2212 grains. These particles are well dispersed and located preferentially at the platelet-like grain boundaries in the superconducting Bi 2212 composites. This is of interest in analogy to the widely studied YBa2Cu3Oy (Y123) superconductor with two-phase microstructure with Y2BaCuO5 (Y211) precipitates, which is known to provide flux pinning and considerable enhancement of the critical current densities (Jc). The superconducting properties of the present Bi 2212 composites with varying amounts of second phase content are assessed by recording M-H loops at different temperatures 5 to 77 K. Critical current densities are found to be non-zero at 5 K in all the samples up to 9 T applied field, suggesting irreversibility fields to be above 9T. A considerable enhancement of Jc and flux pinning force are observed at temperatures 15–50 K, compared to pure 2212 phase at low concentrations (0.1 wt%) of nano WO3 addition in the composites. A minor drop in the superconducting transition temperature Tc (onset) from 90 to 80 K observed in the sample with higher WO3 addition (5 wt%) caused a lowering of flux pinning force at temperatures 50 K and above. Scaling laws of flux pinning show that normal surface pinning is the dominant mechanism in all the samples, which can be attributed to the structural defects at the 2212 platelet boundaries. Flux pinning is observed to be sustained in a broader field range and up to 50 K in all the samples with WO3 addition. This provides evidence that the interfacial defects associated with the second phase (W-alloy) particles, created at the platelet boundaries, are effective in providing flux pinning. [ABSTRACT FROM AUTHOR]

YBa2Cu3Ox (YBCO) thin films were deposited on 14°–22° tilted-axes NdGaO3 (NGO) substrates with pulsed laser deposition. Two orientations of the film are possible due to the presence of symmetrically equivalent (110) and (1 − 1 0) facets on the substrate surface. At high deposition rates, the pseudo-a grains, (100)YBCO||(110)NGO, gradually overgrow the pseudo-c grains, (001)YBCO||(110)NGO, forming high-tilted (tilt angle of the c axis 69°–74°) YBCO films. The substrate tilt angles in the vicinity of 18.43° promote formation of high-tilted films as a result of graphoepitaxial seeding of the pseudo-a grains on the (110) facets on the substrate surface due to the matching of the c lattice constant of the film with the length of the (110) terraces on the substrate surface. The effect of graphoepitaxial seeding was observed for the substrate tilt angles in the range 16°–21°, probably due to undulating edges of steps on the substrate surface. An increase of the deposition rate above a threshold level of ~ 3 nm/s results in a change of the growth mode with the formation of films with smooth surface morphology. The probable reason is a transition from vapor phase epitaxy to vapor–liquid–solid crystallization mechanism. The tilted-axes YBCO films demonstrate superconducting transition temperature superior to standard samples fabricated on (110) NGO substrates. The width of the superconducting transition for tilted-axes films increases due to the suppression of the critical current in the direction normal to the tilt axis. [ABSTRACT FROM AUTHOR]