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Experimental contributors to the field of superconducting materials share their informal views on the subject.

Spatial disorder has been shown to drive two-dimensional (2D) superconductors to an insulating phase through a superconductor-insulator transition (SIT). Numerical calculations predict that with increasing disorder, emergent electronic granularity is expected in these materials-a phenomenon where superconducting (SC) domains on the scale of the material's coherence length are embedded in an insulating matrix and coherently coupled by Josephson tunneling. Here, we present spatially resolved scanning tunneling spectroscopy (STS) measurements of the three-dimensional (3D) superconductor BaPb 1- x Bi x O 3 (BPBO), which surprisingly demonstrate three key signatures of emergent electronic granularity, having only been previously conjectured and observed in 2D thin-film systems. These signatures include the observation of emergent SC domains on the scale of the coherence length, finite energy gap over all space, and strong enhancement of spatial anticorrelation between pairing amplitude and gap magnitude as the SIT is approached. These observations are suggestive of 2D SC behavior embedded within a conventional 3D s -wave host, an intriguing but still unexplained interdimensional phenomenon, which has been hinted at by previous experiments in which critical scaling exponents in the vicinity of a putative 3D quantum phase transition are consistent only with dimensionality d = 2., Competing Interests: The authors declare no competing interest.

A crucial issue in cuprates is the extent and mechanism of the coupling of the lattice to the electrons and the superconductivity. Here we report Cu K edge extended X-ray absorption fine structure measurements elucidating the internal quantum tunneling polaron (iqtp) component of the dynamical structure in two heavily overdoped superconducting cuprate compounds, tetragonal YSr 2 Cu 2.75 Mo 0.25 O 7.54 with superconducting critical temperature, T c = 84 K and hole density p = 0.3 to 0.5 per planar Cu, and the tetragonal phase of Sr 2 CuO 3.3 with T c = 95 K and p = 0.6. In YSr 2 Cu 2.75 Mo 0.25 O 7.54 changes in the Cu-apical O two-site distribution reflect a sequential renormalization of the double-well potential of this site beginning at T c , with the energy difference between the two minima increasing by ∼6 meV between T c and 52 K. Sr 2 CuO 3.3 undergoes a radically larger transformation at T c , >1-Å displacements of the apical O atoms. The principal feature of the dynamical structure underlying these transformations is the strongly anharmonic oscillation of the apical O atoms in a double-well potential that results in the observation of two distinct O sites whose Cu-O distances indicate different bonding modes and valence-charge distributions. The coupling of the superconductivity to the iqtp that originates in this nonadiabatic coupling between the electrons and lattice demonstrates an important role for the dynamical structure whereby pairing occurs even in a system where displacements of the atoms that are part of the transition are sufficiently large to alter the Fermi surface. The synchronization and dynamic coherence of the iqtps resulting from the strong interactions within a crystal would be expected to influence this process., Competing Interests: The authors declare no competing interest., (Copyright © 2020 the Author(s). Published by PNAS.)

The local structure of the highly "overdoped" 95 K superconductor Sr 2 CuO 3.3 determined by Cu K X-ray absorption fine structure (XAFS) at 62 K in magnetically oriented samples shows that 1) the magnetization is perpendicular to the c axis; 2) at these levels of precision the Cu sublattice is tetragonal in agreement with the crystal structure; the O sublattice has 3) continuous -Cu-O- chains that orient perpendicular to an applied magnetic field; 4) approximately half-filled -Cu-O- chains that orient parallel to this field; 5) a substantial number of apical O vacancies; 6) O ions at some apical positions with expanded Cu-O distances; and 7) interstitial positions that imply highly displaced Sr ions. These results contradict the universally accepted features of cuprates that require intact CuO 2 planes, magnetization along the c axis, and a termination of the superconductivity when the excess charge on the CuO 2 Cu ions exceeds 0.27. These radical differences in charge and structure demonstrate that this compound constitutes a separate class of Cu-O-based superconductors in which the superconductivity originates in a different, more complicated structural unit than CuO 2 planes while retaining exceptionally high transition temperatures., Competing Interests: The authors declare no competing interest.

A common characteristic of many "overdoped" cuprates prepared with high-pressure oxygen is T c values ≥ 50 K that often exceed that of optimally doped parent compounds, despite O stoichiometries that place the materials at the edge or outside of the conventional boundary between superconducting and normal Fermi liquid states. X-ray absorption fine-structure (XAFS) measurements at 52 K on samples of high-pressure oxygen (HPO) YSr 2 Cu 2.75 Mo 0.25 O 7.54 , T c = 84 K show that the Mo is in the (VI) valence in an unusually undistorted octahedral geometry with predominantly Mo neighbors that is consistent with its assigned substitution for Cu in the chain sites of the structure. Perturbations of the Cu environments are minimal, although the Cu X-ray absorption near-edge structure (XANES) differs from that in other cuprates. The primary deviation from the crystal structure is therefore nanophase separation into Mo- and Cu-enriched domains. There are, however, indications that the dynamical attributes of the structure are altered relative to YBa 2 Cu 3 O 7 , including a shift of the Cu-apical O two-site distribution from the chain to the plane Cu sites. Another effect that would influence T c is the possibility of multiple bands at the Fermi surface caused by the presence of the second phase and the lowering of the Fermi level., Competing Interests: The authors declare no competing interest.

Ted Geballe has contributed enormously to the knowledge of superconducting materials during an illustrious scientific career spanning seven decades, encompassing groundbreaking discoveries and studies of both so-called conventional and unconventional superconductors. On the year of his 100th birthday, I would like to argue that all superconducting materials that Ted investigated, as well as those he did not, have one thing in common that is not generally recognized: hole carriers. This includes PbTe doped with Tl, for which Ted has proposed that superconductivity is driven by negative-U pairing. I will discuss why hole carriers are necessary for a material to be a superconductor, and the implications of this for the understanding of the fundamental physics of superconductivity. [ABSTRACT FROM AUTHOR]

The phase diagram of BaPb(1-x)Bi(x)O3 exhibits a superconducting dome in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high-resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare with the Ginzburg-Landau coherence length. We find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.

Formulations to determine the electric field and the electrostatic potentials in a thermoelectric couple through solving the Poisson’s equation are introduced in this work. Analytical approximations of the auxiliary energies introduced in the author’s earlier work in the relaxation time approximation of the Boltzmann transport equation are developed based on the coupled equations of heat and electric current. These auxiliary energies are used in the Poisson’s equation at each temperature node along the thermoelectric leg to obtain a set of algebraic equations with the electric field and the electrostatic potentials as unknowns. The algebraic equations are then solved using the derived algorithm and the boundary conditions determined by the continuity and the carrier concentration equations. [ABSTRACT FROM AUTHOR]

Unconventional superconductivity, where electron pairing does not involve electron-phonon interactions, is often attributed to magnetic correlations in a material. Well known examples include high-Tc cuprates and uranium-based heavy fermion superconductors. Less explored are unconventional superconductors with strong spin-orbit coupling, where interactions between spin-polarised electrons and external magnetic field can result in multiple superconducting phases and field-induced transitions between them, a rare phenomenon in the superconducting state. Here we report a magnetic-field driven phase transition in β-PdBi2, a layered non-magnetic superconductor. Our tunnelling spectroscopy on thin PdBi2 monocrystals incorporated in planar superconductor-insulator-normal metal junctions reveals a marked discontinuity in the superconducting properties with increasing in-plane field, which is consistent with a transition from conventional (s-wave) to nodal pairing. Our theoretical analysis suggests that this phase transition may arise from spin polarisation and spin-momentum locking caused by locally broken inversion symmetry, with p-wave pairing becoming energetically favourable in high fields. Our findings also reconcile earlier predictions of unconventional multigap superconductivity in β-PdBi2 with previous experiments where only a single s-wave gap could be detected. β-PdBi2 superconducting properties have been known about since the 1950s, with various works since then indicating the possibility of multiple superconducting gaps and unconventional superconductivity. However, so far only a single gap s-wave superconductivity was detected. Here, using tunnelling spectroscopy under an applied magnetic field, Powell et al observe a transition from s-wave to nodal pairing. [ABSTRACT FROM AUTHOR]

We present two ideas to simplify the measurement and analysis of terahertz time-domain spectroscopic ellipsometry data of ultrathin films. The measurement is simplified by using a specially designed sample holder with mirrors, which can be mounted on a cryostat. It allows us to perform spectroscopic ellipsometry by simply inserting the holder into a conventional terahertz spectroscopy system for measurements in transmission geometry. The analysis of the obtained data is simplified by considering a single interface with a certain sheet conductivity σ s (since the film thickness is significantly smaller than the wavelength of the terahertz light). We demonstrate the application of these ideas by evaluating the sheet conductivities of two perovskite rare-earth nickelate thin films in the temperature range 78–478 K. The use of this particular analytical method and the sample holder design will help to establish terahertz time-domain spectroscopic ellipsometry as a characterization technique for ultrathin films. [ABSTRACT FROM AUTHOR]

The Mott-Ioffe-Regel limit sets the lower bound of the carrier mean free path for coherent quasiparticle transport. Metallicity beyond this limit is of great interest because it is often closely related to quantum criticality and unconventional superconductivity. Progress along this direction mainly focuses on the strange-metal behaviors originating from the evolution of the quasiparticle scattering rate, such as linear-in-temperature resistivity, while the quasiparticle coherence phenomena in this regime are much less explored due to the short mean free path at the diffusive bound. Here we report the observation of quantum oscillations from Landau quantization near the Mott-Ioffe-Regel limit in CaAs3. Despite the insulator-like temperature dependence of resistivity, CaAs3 presents giant magnetoresistance and prominent Shubnikov–de Haas oscillations from Fermi surfaces, indicating highly coherent band transport. In contrast, quantum oscillation is absent in the magnetic torque. The quasiparticle effective mass increases systematically with magnetic fields, manifesting a much larger value than what is expected based on magneto-infrared spectroscopy. This suggests a strong many-body renormalization effect near the Fermi surface. We find that these unconventional behaviors may be explained by the interplay between the mobility edge and the van Hove singularity, which results in the formation of coherent cyclotron orbits emerging at the diffusive bound. Our results call for further study on the electron correlation effect of the van Hove singularity. [ABSTRACT FROM AUTHOR]

Hydride superconductors continue to fascinate the communities of condensed matter physics and material scientists because they host the promising near room-temperature superconductivity. Current research has concentrated on the new hydride superconductors with the enhancement of the superconducting transition temperature (T c). The multiple extreme conditions (high pressure/temperature and magnetic field) will introduce new insights into hydride superconductors. The study of transport properties under very high magnetic fields facilitates the understanding of superconductivity in conventional hydride superconductors. In the present work, we report experimental evidence of an unusual metal state in a newly synthesized cubic A15-type La4H23 that exhibits superconductivity with a T c reaching 105 K at 118 GPa. A large negative magnetoresistance is observed in strong pulsed magnetic fields in the non-superconducting state of this compound below 40 K. Moreover, we construct the full magnetic phase diagram of La4H23 up to 68 T at high pressure. The present work reveals anomalous electronic structural properties of A15-La4H23 under high magnetic fields, and therefore has great importance with regard to advancing the understanding of quantum transport behaviors in hydride superconductors. [ABSTRACT FROM AUTHOR]

Superalloys are indispensable materials for the fabrication of high-temperature components in aircraft engines. The discovery of a novel class of γ/γ′ Co-Al-W alloys has ignited a surge of interest in Co-based superalloys, with the aspiration to transcend the inherent constraints of their Ni-based counterparts. However, the conventional methodologies utilized in the design and advancement of new γ/γ′ Co-based superalloys are frequently characterized by their laborious and resource-intensive nature. In this study, we employed a coupled Density Functional Theory (DFT) and machine learning (ML) approach to predict and analyze the stability of the crucial γ′ phase, which is instrumental in expediting the discovery of γ/γ′ Co-based alloys. A dataset comprised of thousands of reliable formation (Hf) and decomposition (Hd) energies was obtained through high-throughput DFT calculations. Through regression model selection and feature engineering, our trained Random Forest (RF) model achieved prediction accuracies of 98.07% for Hf and 97.05% for Hd. Utilizing the well-trained RF model, we predicted the energies of over 150,000 ternary and quaternary γ′ phases within the Co-Ni-Fe-Cr-Al-W-Ti-Ta-V-Mo-Nb system. The energy analyses revealed that the presence of Ni, Nb, Ta, Ti, and V significantly reduced the Hf and the Hd of γ′, while Mo and W deteriorate the stability by increasing both energy values. Interestingly, although Al reduces the Hf, it increases Hd, thereby adversely affecting the stability of γ′. Applying domain-specific screening based on our knowledge, we identified 1049 out of >150,000 compositions likely to form stable γ′ phases, predominantly distributed across 11 Al-containing systems and 25 Al-free systems. Combining the analysis of CALPHAD method, we experimentally synthesized two new Co-based alloys with γ/γ′ dual-phase microstructures, corroborating the reliability of our theoretical prediction model. [ABSTRACT FROM AUTHOR]

We present an exploration of the effect of electron-phonon coupling and broken inversion symmetry on the electronic and thermal properties of the semimetal LaRhGe3. Our transport measurements reveal evidence for electron-hole compensation at low temperatures, resulting in a large magnetoresistance of 3000% at 1.8 K and 14 T. The carrier concentration is on the order of 1021/cm3 with high carrier mobilities of 2000 cm2/Vs. When coupled to our theoretical demonstration of symmetry-protected almost movable Weyl nodal lines, we conclude that LaRhGe3 supports a Weyl semimetallic state. We discover superconductivity in this compound with a Tc of 0.39(1) K and Bc(0) of 2.2(1) mT, with evidence from specific heat and transverse-field muon spin relaxation. We find an exponential dependence in the normal state electrical resistivity below ~50 K, while Seebeck coefficient and thermal conductivity measurements each reveal a prominent peak at low temperatures, indicative of strong electron-phonon interactions. To this end, we examine the temperature-dependent Raman spectra of LaRhGe3 and find that the lifetime of the lowest energy A1 phonon is dominated by phonon-electron scattering instead of anharmonic decay. We conclude that LaRhGe3 has strong electron-phonon coupling in the normal state, while the superconductivity emerges from weak electron-phonon coupling. These results open up the investigation of electron-phonon interactions in the normal state of superconducting non-centrosymmetric Weyl semimetals. [ABSTRACT FROM AUTHOR]

Crystalline solids typically show robust long-range structural ordering, vital for their remarkable electronic properties and use in functional electronics, albeit with limited customization space. By contrast, synthetic molecular systems provide highly tunable structural topologies and versatile functionalities but are often too delicate for scalable electronic integration. Combining these two systems could harness the strengths of both, yet realizing this integration is challenging owing to distinct chemical bonding structures and processing conditions. Two-dimensional atomic crystals comprise crystalline atomic layers separated by non-bonding van der Waals gaps, allowing diverse atomic or molecular intercalants to be inserted without disrupting existing covalent bonds. This enables the creation of a diverse set of layered hybrid superlattices (LHSLs) composed of alternating crystalline atomic layers of variable electronic properties and self-assembled atomic or molecular interlayers featuring customizable chemical compositions and structural motifs. Here we outline strategies to prepare LHSLs and discuss emergent properties. With the versatile molecular design strategies and modular assembly processes, LHSLs offer vast flexibility for weaving distinct chemical constituents and quantum properties into monolithic artificial solids with a designable three-dimensional potential landscape. This opens unprecedented opportunities to tailor charge correlations, quantum properties and topological phases, thereby defining a rich material platform for advancing quantum information science.Methods to manufacture layered hybrid superlattices composed of alternating crystalline atomic layers and self-assembled atomic or molecular interlayers are described, to make use of their combined strengths and produce designable quantum solids. [ABSTRACT FROM AUTHOR]

Strain engineering is a widely used technique for enhancing the mobility of charge carriers in semiconductors, but its effect is not fully understood. In this work, we perform first-principles calculations to explore the variations of the mobility of electrons and holes in silicon upon deformation by uniaxial strain up to 2% in the [100] crystal direction. We compute the π11 and π12 electron piezoresistances based on the low-strain change of resistivity with temperature in the range 200 K to 400 K, in excellent agreement with experiment. We also predict them for holes which were only measured at room temperature. Remarkably, for electrons in the transverse direction, we predict a minimum room-temperature mobility about 1200 cm2 V−1 s−1 at 0.3% uniaxial tensile strain while we observe a monotonous increase of the longitudinal transport, reaching a value of 2200 cm2 V−1 s−1 at high strain. We confirm these findings experimentally using four-point bending measurements, establishing the reliability of our first-principles calculations. For holes, we find that the transport is almost unaffected by strain up to 0.3% uniaxial tensile strain and then rises significantly, more than doubling at 2% strain. Our findings open new perspectives to boost the mobility by applying a stress in the [100] direction. This is particularly interesting for holes for which shear strain was thought for a long time to be the only way to enhance the mobility. [ABSTRACT FROM AUTHOR]

The early work on superconductivity in layered transition metal dichalcogenides, the prototypical two-dimensional material, at Stanford in the Geballe group is reviewed. Specific heat played an important role as a characterization tool. [ABSTRACT FROM AUTHOR]

Homogeneous mixed-valence (MV) behaviour is one of the most intriguing phenomena of f-electron systems. Despite extensive efforts, a fundamental aspect which remains unsettled is the experimental determination of the limiting cases for which MV emerges. Here we address this question for SmB6, a prototypical MV system characterized by two nearly-degenerate Sm2+ and Sm3+ configurations. By combining angle-resolved photoemission spectroscopy (ARPES) and x-ray absorption spectroscopy (XAS), we track the evolution of the mean Sm valence, vSm, in the SmxLa1−xB6 series. Upon substitution of Sm ions with trivalent La, we observe a linear decrease of valence fluctuations to an almost complete suppression at x = 0.2, with vSm ~ 2; surprisingly, by further reducing x, a re-entrant increase of vSm develops, approaching the value of vimp ~ 2.35 in the dilute-impurity limit. Such behaviour departs from a monotonic evolution of vSm across the whole series, as well as from the expectation of its convergence to an integer value for x → 0. Our ARPES and XAS results, complemented by a phenomenological model, demonstrate an unconventional evolution of the MV character in the SmxLa1−xB6 series, paving the way to further theoretical and experimental considerations on the concept of MV itself, and its influence on the macroscopic properties of rare-earth compounds in the dilute-to-intermediate impurity regime. This study reveals a non-monotonic evolution of the mixed-valence character in the SmxLa1−xB6 series, with near-complete suppression of valence fluctuations in the intermediate substitution regime, followed by a re-emergent mixed-valence behavior in the dilute-impurity limit. [ABSTRACT FROM AUTHOR]

The probing of coherent lattice vibrations in solids has conventionally been carried out using time-resolved transient optical spectroscopy, with which only the relative oscillation amplitude can be obtained. Using time-resolved X-ray techniques, absolute electron–phonon coupling strength could be extracted. However, the complexity of such an experiment renders it impossible to be carried out in conventional laboratories. Here we demonstrate that the electron–phonon, anharmonic phonon–phonon coupling and their relaxation dynamics can be probed in real time using high-harmonic spectroscopy. Our technique is background-free and has extreme sensitivity directly in the energy domain. In combination with the optical deformation potential calculated from density functional perturbation theory and the absolute energy modulation depth, our measurement reveals the maximum displacement of neighbouring oxygen atoms in α-quartz crystal to tens of picometres in real space. By employing a straightforward and robust time-windowed Gabor analysis for the phonon-modulated high-harmonic spectrum, we successfully observe channel-resolved four-phonon scattering processes in such highly nonlinear interactions. Our work opens a new realm for the accurate measurement of coherent phonons and their scattering dynamics, which allows for potential benchmarking ab initio calculations in solids. High-harmonic spectroscopy is employed to investigate the electron–phonon, anharmonic phonon–phonon coupling, and their relaxation dynamics in solids. It reveals the maximum displacement of neighbouring oxygen atoms in α-quartz crystal to tens of picometres in real space. [ABSTRACT FROM AUTHOR]

Chiral superconductors, a unique class of unconventional superconductors in which the complex superconducting order parameter winds clockwise or anticlockwise in the momentum space1, represent a topologically non-trivial system with intrinsic time-reversal symmetry breaking (TRSB) and direct implications for topological quantum computing2,3. Intrinsic chiral superconductors are extremely rare, with only a few arguable examples, including UTe2, UPt3 and Sr2RuO4 (refs. 4–7). It has been suggested that chiral superconductivity may exist in non-centrosymmetric superconductors8,9, although such non-centrosymmetry is uncommon in typical solid-state superconductors. Alternatively, chiral molecules with neither mirror nor inversion symmetry have been widely investigated. We suggest that an incorporation of chiral molecules into conventional superconductor lattices could introduce non-centrosymmetry and help realize chiral superconductivity10. Here we explore unconventional superconductivity in chiral molecule intercalated TaS2 hybrid superlattices. Our studies reveal an exceptionally large in-plane upper critical field Bc2,|| well beyond the Pauli paramagnetic limit, a robust π-phase shift in Little–Parks measurements and a field-free superconducting diode effect (SDE). These experimental signatures of unconventional superconductivity suggest that the intriguing interplay between crystalline atomic layers and the self-assembled chiral molecular layers may lead to exotic topological materials. Our study highlights that the hybrid superlattices could lay a versatile path to artificial quantum materials by combining a vast library of layered crystals of rich physical properties with the nearly infinite variations of molecules of designable structural motifs and functional groups11.By incorporating chiral molecules into conventional superconductor lattices such as TaS2 to form a hybrid superlattice, non-centrosymmetry could be introduced and can be shown to help lead to unconventional superconductivity. [ABSTRACT FROM AUTHOR]

Searching for topological superconductors that host topological charge-neutral Majorana zero-modes at edges has become a central problem in condensed matter research due to their potential applications for quantum computations. Meanwhile, electron correlations in solid-state materials enhance quantum fluctuations and give rise to various quantum many-body phases. Whether these electron correlations alone would lead to topological superconductivity is a fundamentally important open problem. Here, we theoretically find the correlation-driven topological superconductivity in a class of Kondo lattice materials. Therein, the odd-parity Kondo hybridization mediates ferromagnetic spin-spin coupling and leads to spin-triplet pairing between local moments. Triplet p ± i p ′ -wave topological superconductivity with Majorana zero modes at edges is reached when Kondo hybridization co-exists with the triplet pairings. Our results offer a detailed understanding of the experimental observations on UTe2, a ferromagnetic heavy-electron triplet superconductor. Our approach to topological superconductivity shows advantages over the heterostructure approach by proximity effect. The authors find theoretically topological superconductivity in a class of Kondo lattice materials driven by strongly correlated Kondo effects with odd-parity Kondo hybridization. Their results offer a detailed understanding of UTe2, a ferromagnetic heavy-electron triplet superconductor, as well as a guiding principle in the search for topological superconductors. [ABSTRACT FROM AUTHOR]

In this work, we presented our results on the electrical and magnetoresistance characteristics of La0.7Ca0.1Pb0.2Mn1-2xAlxSnxO3 (x equal to 0 and 0.025) prepared using the sol–gel method. X-ray diffraction (XRD) analysis revealed that all samples crystallize in Rhombohedral structure with R-3c space group. In addition, to obtain further information regarding the electrical properties, we performed resistance versus temperature ρ (T) measurements under different applied magnetic fields using a standard four-probe technique. The resistivity data, represented as ρ (μ0H, T), indicated the presence of a transition from metal to semiconductor state. As the magnetic field increases, the maximum resistivity values decrease, and the temperature (TM-SC) at which the transition from insulator to metal occurs rises. In the temperature range where T is less than TM–SC, the electrical resistivity ρ (T) was modeled as ρ(T) = ρ0 + ρ2T2 + ρ4.5T4.5, signifying that the transport behavior is influenced by a combination of interactions involving electron–magnon, electron–phonon and electron–electron scattering processes. Conversely, in the temperature range exceeding TM–SC, the transport mechanism was elucidated through the utilization of adiabatic small polaron hopping and variable-range hopping models. To improve understanding of the variations in the resistivity profile across the temperature range, ρ (T) was fitted using the percolation model. Additionally, research was conducted on the magnetoresistance effect (MR %). The highest magnetoresistance values are observed around the temperature TM–SC. Highlights: La0.7Ca0.1Pb0.2Mn1-2xAlxSnxO3 was synthesized using the sol–gel method. X-ray diffraction (XRD) analysis confirmed that all samples crystallize in a Rhombohedral structure with an R-3c space group. The resistivity data, denoted as ρ (μ0H, T), showed a transition from a metallic to a semiconducting state. For temperatures below TM–SC, the electrical resistivity ρ (T) was described by the equation ρ(T) = ρ0 + ρ2T2 + ρ4.5T4.5, indicating that the transport properties are influenced by electron–magnon, electron–phonon, and electron–electron scattering processes. For temperatures above TM–SC, the transport mechanism was explained using adiabatic small polaron hopping and variable-range hopping models. Near the critical temperature, the resistivity was modeled using the percolation model. The highest magnetoresistance values were observed around the temperature TM–SC. [ABSTRACT FROM AUTHOR]

The most recent research and developments are driven by colossal permittivity (CP) materials due to their potential use in modern microelectronics and high-energy density storage applications. Even though, to date, many CP materials have been discovered, the task of developing them with the required high performance remains highly challenging. We present a tangible example, polycrystalline ZnO ceramic, that presents a highly frequency-stable CP (> 104) as well as a low dielectric loss (~ 0.3) over a broad temperature range from 278 to 433 K. Multifunctional polycrystalline ZnO nanoceramics are prepared through one-pot hydrothermal route and sintered at 300 °C and 600 °C. The highly magnified scanning electron microscopic images reveal excellent grain growth at high temperature. Temperature-dependent impedance spectroscopy is employed for pellet sintered at (600 °C) to explore different conduction mechanisms at various temperature ranges. The distribution of relaxation times (DRT) method is used to design the best equivalent circuit model for fitting impedance data. The non-Debye behavior of real permittivity (ɛ′) is well explained by fitting with Cole–Cole formalism. The change in the conduction mechanism is estimated around 343 K, and an adiabatic polaronic model is used to estimate activation energies of cations through different electroactive regions. The correlate barrier hopping (CBH) model is applied to measure electrical trapping parameters (like binding energy, hopping distance, barrier height, etc.) at various temperatures. Our finding presents a systematic approach toward frequency-independent ZnO ceramics with a stable colossal permittivity which can potentially be applied to develop energy storage devices. [ABSTRACT FROM AUTHOR]

Direct growth of oxide film on silicon is usually prevented by extensive diffusion or chemical reaction between silicon (Si) and oxide materials. Thermodynamic stability of binary oxides is comprehensively investigated on Si substrates and shows possibility of chemical reaction of oxide materials on Si surface. However, the thermodynamic stability does not include any crystallographic factors, which is required for epitaxial growth. Adsorption energy evaluated by total energy estimated with the density functional theory predicted the orientation of epitaxial film growth on Si surface. For lower computing cost, the adsorption energy was estimated without any structural optimization (simple total of energy method). Although the adsorption energies were different on simple ToE method, the crystal orientation of epitaxial growth showed the same direction with/without the structural optimization. The results were agreed with previous simulations including structural optimization. Magnesium oxide (MgO), as example of epitaxial film, was experimentally deposited on Si substrates and compared with the results from the adsorption evaluation. X-ray diffraction showed cubic on cubic growth [MgO(100)//Si(100) and MgO(001)//Si(001)] which agreed with the results of the adsorption energy. [ABSTRACT FROM AUTHOR]

In this report, a solid-state approach was followed to synthesize a new double perovskite MgBi1.2Fe0.8TiO6. The initial inspection of the material was carried out through XRD analysis and found Arruvillias-type compounds Am−1BmO3m+1, m = 5. The tolerance factor (τ ~ 0.8) was calculated by approximation tools and reveals the presence of structural distortion. The SEM image suggests the development of polycrystalline behavior and shows av. grain size ~ 1.3 μm as compared to (~ 14 nm) av. crystallites. The UV–visible absorbance nature shows a higher threshold wavelength of about 657 nm and a direct bandgap of ~ 2.10 eV suggesting that the material has good absorbance features over IR and visible emission. The compound exhibits av. the dielectric constant, ~ 747, and low loss ~ 0.360 in ambient conditions, while the transition temperature appears above ~ 234 °C at 100 Hz applied field. Heat-dependent carrier mobility indicates bulk-grain and their boundary effect's contribution to semiconductor behavior and non-Debye relaxation mechanism. The non-zero electric polarization and ferromagnetism are also observed in the substance. The synthesized sample can be a promising material in energy and data-storing electronic equipment. [ABSTRACT FROM AUTHOR]

A new Ba2CuO4-y superconductor with critical temperature (Tc) exceeding 70 K was discovered. The X-ray absorption measurement gives evidence that this cuprate resembles La2CuO4 but is doped with a fairly large amount of holes, while in contrast to the so far known hole-doped high-Tc cuprates, the new cuprate possesses a much shorter local apical oxygen distance as well as much expanded in-plane Cu–O bond, leading to unprecedented compressed local octahedron. In compressed local octahedron, the Cu3d3z2–r2 orbital level will be lifted above the Cu3dx2-y2 orbital level with more three-dimensional features, implying that pairing symmetry may carry admixtures from more than one gap, suggesting that Ba2CuO4-y composed of alkaline earth copper oxides that are the essential elements to form cuprate superconductors may belong to a new branch of cuprate superconductors. [ABSTRACT FROM AUTHOR]

Due to the strong interactions from multiple degrees of freedom at the interfaces, electron-correlated oxide heterostructures have provided a promising platform for creating exotic quantum states. Understanding and controlling the coupling effects at the oxide interface are prerequisites for designing emergent interfacial phases with desired functionalities. Here, we report the dimensional control of the interface coupling-induced ferromagnetic (FM) phase in perovskite-CaRuO3/infinite-layered-SrCuO2 superlattices. Structural analysis reveals the occurrence of chain-type to planar-type structural transitions for the SrCuO2 layer as the layer thickness increases. The Hall and magnetoresistance measurements indicate the appearance of an interfacial FM state in the originally paramagnetic CaRuO3 layers when the CaRuO3 layer is in proximity to the chain-type SrCuO2 layers; this superlattice has the highest Curie temperature of ~75 K and perpendicular magnetic anisotropy. Along with the thickness-driven structural transition of the SrCuO2 layers, the interfacial FM order gradually deteriorates and finally disappears. As shown by the X-ray absorption results, the charge transfer at the CaRuO3/chain-SrCuO2 and CaRuO3/plane-SrCuO2 interfaces are different, resulting in dimensional control of the interfacial magnetic state. The results from our study can be used to facilitate a new method to manipulate interface coupling and create emergent interfacial phases in oxide heterostructures. Harnessing Quantum States: A Breakthrough in Oxide Heterostructures Perovskite transition-metal oxides, known for their complex electron interactions, exhibit unique physical properties like superconductivity and magnetoresistance. However, layering these materials can result in new, unexpected behaviors at their interfaces. This study focuses on a layered structure of perovskite ruthenate and strontium cuprate. The research shows that by controlling the thickness of SCO layers in CRO/SCO superlattices, it is possible to induce ferromagnetism in CRO, which normally does not exhibit this property. The authors conclude that this manipulation of interface coupling can lead to new interfacial phases with potential applications in spintronics. The findings open up possibilities for future research into the control of quantum phases in complex oxide materials. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author. In this paper, we report the dimensional control of the interface coupling-induced ferromagnetic phase in perovskite-CaRuO3/infinite-layered-SrCuO2 superlattices. The Hall and magnetoresistance measurements indicate the appearance of an interfacial ferromagnetic state in the originally paramagnetic CaRuO3 layers when the CaRuO3 layer is in proximity to the chain-type SrCuO2 layers; this superlattice has the highest Curie temperature of ~75 K and perpendicular magnetic anisotropy. Along with the thickness-driven structural transition from chain-type to planar-type of the SrCuO2 layers, the interfacial ferromagnetic order gradually deteriorates and finally disappears. [ABSTRACT FROM AUTHOR]

Controlling and understanding electron correlations in quantum matter is one of the most challenging tasks in materials engineering. In the past years a plethora of new puzzling correlated states have been found by carefully stacking and twisting two-dimensional van der Waals materials of different kind. Unique to these stacked structures is the emergence of correlated phases not foreseeable from the single layers alone. In Ta-dichalcogenide heterostructures made of a good metallic "1H"- and a Mott insulating "1T"-layer, recent reports have evidenced a cross-breed itinerant and localized nature of the electronic excitations, similar to what is typically found in heavy fermion systems. Here, we put forward a new interpretation based on first-principles calculations which indicates a sizeable charge transfer of electrons (0.4-0.6 e) from 1T to 1H layers at an elevated interlayer distance. We accurately quantify the strength of the interlayer hybridization which allows us to unambiguously determine that the system is much closer to a doped Mott insulator than to a heavy fermion scenario. Ta-based heterolayers provide therefore a new ground for quantum-materials engineering in the regime of heavily doped Mott insulators hybridized with metallic states at a van der Waals distance. Recent experiments reported the Kondo effect in 1H/1T dichalcogenide hetero-bilayers. Crippa et al. re-examine this interpretation using ab initio calculations and dynamical mean-field theory demonstrating strong charge transfer sensitive to the interlayer separation, indicative of a doped Mott insulator regime. [ABSTRACT FROM AUTHOR]

Half‐metallic ferromagnets (HMFs) are highly desirable materials for applications in spintronics because of their semiconducting behavior for one spin projection and metallic nature for the other. To operate spintronic devices at room temperature (RT), HMFs should simultaneously have a large saturation magnetization (MS), high magnetic Curie temperature (TC), and a wide half‐metallic gap. However, HMFs that simultaneously fulfill these three criteria are rare. In this work, we report for the first time on the ferrimagnetic double perovskite oxides of Sr2CrHfO6 (SCHO) with a magnetic TC up to 545 K due to the strong Cr3+(↑)Cr4+(↓) antiferromagnetic spin interactions. The combined experimental results confirmed that the SCHO powders crystallized in an orthogonal crystal structure with Pnma symmetry. The SEM images demonstrate that the powders exhibit a spherical morphology with particle sizes between 150 and 250 nm. XPS spectra verified the presence of Sr2+, Cr 3+/Cr4+, and Hf4+/Hfx+ (x < 4) ions in the SCHO powder. Oxygen was present as lattice oxygen and adsorbed oxygen species. At 2 K, the SCHO powder exhibited ferrimagnetic behavior with MS of 0.11 μB/f. u and a magnetic coercive field of 290 Oe. The SCHO ceramics displayed a normal butterfly‐like magnetoresistance‐magnetic field (MR‐H) curve at 2 K due to the intergranular tunneling effect, and the MR (2 K, 7 T) value was −2.05%. The temperature dependence of the resistivity of the SCHO ceramics revealed their semiconducting nature, and the electrical transport data in the temperature range 2−800 K were well fitted by the Mott's variable‐range hopping model, thermal activation model, and small polaron hopping model. Optical measurements demonstrate that the SCHO powders have a direct optical bandgap of 2.25 eV in the visible light window. Having both high TC and a direct optical bandgap (2.25 eV) makes SCHO oxides attractive for use in advanced spintronic devices and solar cells. [ABSTRACT FROM AUTHOR]

Erbium-doped Ni-Cu nanoferrites have been prepared by conventional citrate-gel auto-combustion process. The XRD spectra validated the development of the crystalline phase, tetragonal structure in the pure specimen and the progressive shift to the cubic system of erbium-doped samples. The microstructural analysis was carried out using the scanning electron microscopy (SEM) technique, and elemental mapping images confirmed the elements in the chemical composition. With the help of an LCR meter at ambient temperature, the frequency-dependent various dielectric parameters were measured. The observed dielectric constant and AC conductivity have shown the as-expected behaviour of ferrite samples. In the high-frequency domain, the Er3+ doping has enhanced the dielectric constant, which varies between 12.65 and 13.45 at 1 MHz and 12.57 and 13.35 at 2 MHz. The AC conductivity was noticed between 1.487 and 1.934 S/cm at 1 MHz and 2.222 and 3.090 S/cm at 2 MHz. The extracted values of grain boundary and grain resistances from cole–cole plots were found in the range of 7.81 × 107 to 12.60 × 107 Ω and 4.73 × 106 to 5.61 × 106 Ω and for pure sample 17.6 × 107 Ω and 4.5 × 106 Ω, which reveals that the resistance due to grain boundaries is more dominating than the grains. [ABSTRACT FROM AUTHOR]

In this work, the full-Heusler GaFeCo 2 is studied using the first-principles method based on density functional theory with the generalized gradient approximation (GGA and GGA+U) and Monte Carlo simulation. The unit cell parameter is optimized, and then the stability of the GaFeCo 2 compound is checked through its negative formation energy E f . The electronic density of states and the electronic band structure show the metallic behavior of GaFeCo 2 . The magnetic moments of the material are investigated, and Fe and Co atoms have the spin states ( S = ± 5 2 ; ± 3 2 ; ± 1 2 ) and ( σ = ± 3 2 ; ± 1 2 ), respectively. In order to perform Monte Carlo simulation, the exchange interactions J Co - Co , J Co - Fe , and J Fe - Fe are estimated based on energy calculations. Thermal magnetization, magnetic susceptibility, and magnetocaloric effects, such as magnetic entropy change and relative cooling power (RCP), are calculated. It is found that GaFeCo 2 is a ferromagnetic material with high Curie temperature T c = 1120 ∘ K and an RCP of about 7.5 J/Kg for a magnetic field of 5T. These results suggest that GaFeCo 2 is a promising candidate for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

We report on the structural, electrical and magnetic measurements in as-grown polycrystalline samples of Pb10−xCux(PO4)6O. This compound has been recently reported to be a room temperature superconductor. Our as-grown specimen has excellent XRD matching with the original submission of Lee et al. This sample has 1.5% of Cu2S as an impurity phase. A resistive transition around 380 K, possibly corresponding to structural transitions of Cu2S, is observed. No evidence of superconducting to normal state transitions in I–V characteristics at room temperature is obtained. Magnetization measurements show linear diamagnetic behavior that cannot be associated with the superconducting state. Hall measurements provide evidence of hole doping through Cu substitution. In summary, we find no evidence for room temperature ambient pressure superconductivity in Cu doped lead apatite Pb10−xCux(PO4)6O. [ABSTRACT FROM AUTHOR]

Sb is a three-dimensional Peierls insulator. The Peierls instability gives rise to doubling of the translational period along the [111] direction and alternating van der Waals and covalent bonding between (111) atomic planes. At the (111) surface of Sb, the Peierls condition is violated, which in theory can give rise to properties differing from the bulk. The atomic and electronic structure of the (111) surface of Sb have been simulated by density functional theory calculations. We have considered the two possible (111) surfaces, containing van der Waals dangling bonds or containing covalent dangling bonds. In the models, the surfaces are infinite and the structure is defect free. Structural optimization of the model containing covalent dangling bonds results in strong deformation, which is well described by a topological soliton within the Su–Schrieffer–Heeger model centered about 25 Å below the surface. The electronic states associated with the soliton see an increase in the density of states (DOS) at the Fermi level by around an order of magnitude at the soliton center. Scanning tunneling microscopy and spectroscopy (STM/STS) measurements reveal two distinct surface regions, indicating that there are different surface regions cleaving van der Waals and covalent bonds. The DFT is in good agreement with the STM/STS experiments. [ABSTRACT FROM AUTHOR]

A unified and empirically adequate microscopic theory of novel pseudogap phenomena and Bose-liquid superconductivity and superfluidity in high- T c cuprates and other systems is developed based on the original ideas of the pseudogap state and unusual superconducting/superfluid states of matter. This theory establishes the following laws: (i) the high- T c cuprates and other systems with low Fermi energies ε F ∼ ε A (where ε A is the energy of the attractive interaction between fermionic quasiparticles) are bosonic superconductors and superfluids exhibiting pseudogap behavior above the superconducting/superfluid transition temperature T c and a λ -like phase transition at T c , (ii) the pseudogap state and bosonic Cooper pairs in such systems (with ε F ≲ 2 ε A and Bardeen–Cooper–Schrieffer (BCS)-like gap Δ F ≳ 0.17 ε F ) are formed above T c , (iii) only a minority of preformed bosons condenses into a Bose superfluid at T c and (iv) only the systems with ε F > > ε A > > Δ F become BCS-type conventional or topological fermionic superconductors and superfluids. A modified BCS-like model describes the precursor Cooper pairing of fermionic quasiparticles and the formation of bosonic Cooper pairs above T c . The criteria for the bosonization of Cooper pairs and fermion–boson transitions are formulated. The mean-field theory describing new laws of condensation of attracting bosons into Bose superfluids below T c is presented. The proposed microscopic theory explains all the emerging pseudogap behaviors and unusual superconducting/superfluid states and properties of high- T c materials and other systems. In high- T c cuprates, the unconventional electron–phonon interactions and polaronic effects give rise to in-gap states, Fermi-surface reconstruction, two distinct pseudogaps and unusual normal-state properties, a quantum critical point and crossover from BCS superconductivity to Bose-liquid superconductivity. The theory of three-dimensional (3D) and two-dimensional (2D) Bose superfluids describes fairly well the novel superconducting states (i.e., the so-called A and B phases below T c and an extended A phase and related vortex-like state above T c ) and properties of high- T c cuprates (e.g., λ -like transition at T c , first-order phase transition at lower temperatures and other unusual features) in accordance with the experimental data. The reasons for suppression and enhancement of superconductivity by disorders in high- T c cuprates are discussed. Strongly enhanced 2D Bose-liquid superconductivity emerging within a 3D cuprate superconductor (with the highest bulk T c ) persists up to room temperature in multi-lamellar blocks and at grain boundaries and interfaces. Most enhanced 3D Bose-liquid superconductivity can emerge at room temperature in high- T c hydrides under high pressures. Superconducting/superfluid states and properties of heavy-fermion and organic compounds, ruthenate (Sr 2 RuO 4) and possibly high- T c hydrides, quantum liquids ( 3 He and 4 He ) and atomic Fermi gases are also well explained by the proposed theory of Bose superfluids. Finally, new criteria and principles of unconventional superconductivity and superfluidity are formulated. [ABSTRACT FROM AUTHOR]

We have successfully synthesized three osmium-based hexagonal Laves compounds ROs2 (R = Sc, Y, Lu), and discussed their physical properties. LeBail refinement of pXRD data confirms that all compounds crystallize in the hexagonal centrosymmetric MgZn2-type structure (P63/mmc, No. 194). The refined lattice parameters are a = b = 5.1791(1) Å and c = 8.4841(2) Å for ScOs2, a = b = 5.2571(3) Å and c = 8.6613(2) Å for LuOs2 and a = b = 5.3067(6) Å and c = 8.7904(1) Å for YOs2. ROs2 Laves phases can be viewed as a stacking of kagome nets interleaved with triangular layers. Temperature-dependent magnetic susceptibility, resistivity and heat capacity measurements confirm bulk superconductivity at critical temperatures, Tc, of 5.36, 4.55, and 3.47 K for ScOs2, YOs2, and LuOs2, respectively. We have shown that all investigated Laves compounds are weakly-coupled type-II superconductors. DFT calculations revealed that the band structure of ROs2 is intricate due to multiple interacting d orbitals of Os and R. Nonetheless, the kagome-derived bands maintain their overall shape, and the Fermi level crosses a number of bands that originate from the kagome flat bands, broadened by interlayer interaction. As a result, ROs2 can be classified as (breathing) kagome metal superconductors. [ABSTRACT FROM AUTHOR]

Increasing the carrier density in a Mott insulator by chemical doping gives rise to a generic superconducting dome in high temperature superconductors. An intriguing question is whether a second superconducting dome may exist at higher dopings. Here we heavily overdope La2-xSrxCuO4 (0.45 ≤ x ≤ 1.0) and discover an unprecedented reentrance of interface superconductivity in La2-xSrxCuO4 /La2CuO4 heterostructures. As x increases, the superconductivity is weakened and completely fades away at x = 0.8; but it revives at higher doping and fully recovers at x = 1.0. This is shown to be correlated with the suppression of the interfacial charge transfer around x = 0.8 and the weak-to-strong localization crossover in the La2-xSrxCuO4 layer. We further construct a theoretical model to account for the sophisticated relation between charge localization and interfacial charge transfer. Our work advances both the search for and control of new superconducting heterostructures. The authors study interface superconductivity in over-doped La2-xSrxCuO4/La2CuO4 heterostructures. As x increases, the superconductivity is killed at x = 0.8 but fully recovers at x = 1.0, a "re-entrant" superconductivity. [ABSTRACT FROM AUTHOR]

The recent discovery of superconductivity in infinite-layer nickelates generates tremendous research endeavors, but the ground state of their parent compounds is still under debate. Here, we report experimental evidence for the dominant role of Kondo scattering in the underdoped Nd1−xSrxNiO2 thin films. A resistivity minimum associated with logarithmic temperature dependence in both longitudinal and Hall resistivities are observed in the underdoped Nd1−xSrxNiO2 samples before the superconducting transition. At lower temperatures down to 0.04 K, the resistivities become saturated, following the prediction of the Kondo model. A linear scaling behavior |$\sigma _{{\boldsymbol{xy}}}^{{{\bf AHE}}}{\rm{\ }}\sim{\rm{\ }}{\sigma }_{{\boldsymbol{xx}}}$| between anomalous Hall conductivity |$\sigma _{{\boldsymbol{xy}}}^{{\bf{AHE}}}$| and conductivity |${\sigma }_{{\boldsymbol{xx}}}{\rm{\ }}$| is revealed, verifying the dominant Kondo scattering at low temperature. The effect of weak (anti-)localization is found to be secondary. Our experiments can help in clarifying the basic physics in the underdoped Nd1−xSrxNiO2 infinite-layer thin films. [ABSTRACT FROM AUTHOR]

Interlayer decoupling plays an essential role in realizing unprecedented properties in atomically thin materials, but it remains relatively unexplored in the bulk. It is unclear how to realize a large crystal that behaves as its monolayer counterpart by artificial manipulation. Here, we construct a superlattice consisting of alternating layers of NbSe2 and highly porous hydroxide, as a proof of principle for realizing interlayer decoupling in bulk materials. In (NaOH)0.5NbSe2, the electric decoupling is manifested by an ideal 1D insulating state along the interlayer direction. Vibration decoupling is demonstrated through the absence of interlayer models in the Raman spectrum, dominant local modes in heat capacity, low interlayer coupling energy and out-of-plane thermal conductivity (0.28 W/mK at RT) that are reduced to a few percent of NbSe2's. Consequently, a drastic enhancement of CDW transition temperature (>110 K) and Pauling-breaking 2D superconductivity is observed, suggesting that the bulk crystal behaves similarly to an exfoliated NbSe2 monolayer. Our findings provide a route to achieve intrinsic 2D properties on a large-scale without exfoliation. Interlayer decoupling plays an essential role in realizing unprecedented properties. Here, authors construct a superlattice consisting of alternating layers of NbSe2 and highly porous hydroxide, realizing interlayer decoupling and thus realizing exotic monolayer behaviors in bulk materials. [ABSTRACT FROM AUTHOR]

Discovery of novel materials is slow but necessary for societal progress. Here, we demonstrate a closed-loop machine learning (ML) approach to rapidly explore a large materials search space, accelerating the intentional discovery of superconducting compounds. By experimentally validating the results of the ML-generated superconductivity predictions and feeding those data back into the ML model to refine, we demonstrate that success rates for superconductor discovery can be more than doubled. Through four closed-loop cycles, we report discovery of a superconductor in the Zr-In-Ni system, re-discovery of five superconductors unknown in the training datasets, and identification of two additional phase diagrams of interest for new superconducting materials. Our work demonstrates the critical role experimental feedback provides in ML-driven discovery, and provides a blueprint for how to accelerate materials progress. [ABSTRACT FROM AUTHOR]

Barium titanate ceramics with A- site and B-site substitutions are intriguing alternative to lead-based Pb (Zr, Ti) O3 (PZT) because of its comparable properties to soft-PZTs. In this paper, (BaxCa1-xSn0.09 Ti0.91) O3 (x = 0.0525, 0.0575, 0.060) ceramics are prepared using a solid-state reaction technique followed by microwave sintering at 1350 °C for 30 minutes. Structural and electrical properties are investigated. X -ray diffraction shows that the compositions exhibit a tetragonal crystal structure having P4mm symmetry. Temperature dependent dielectric constant measurements in the temperature range of 25 °C to 120 °C shows high dielectric constant of 26250 at 40kHz for BCST ceramics with x=0.0525 and the Curie temperature Tc increases with Ca concentration. The results of dielectric measurements as a function of frequency are also reported. The dielectric loss (tan δ) values in the temperature range 25 °C to 120 °C are observed to be less than 0.03, for all BCST ceramics. The AC conductivity, impedance spectroscopy studies and the conduction mechanism on the basis of Arrhenius plot are discussed in the above-mentioned temperature range. [ABSTRACT FROM AUTHOR]

Using the intercalation technology, a biintercalated clathrate InSe <2 >+3>> was formed in which the guest components are placed in separate layers and alternately stage-ordered. Confirmation of this was obtained based on analysis of X-ray diffraction spectra for the initial single crystal and the single crystal intercalated with a ferroelectric and biintercalant. Due to weak interactions between the semiconductor matrix and guest components, periodic potential barriers of different natures (ferroelectric and ferromagnetic) were formed. This allowed observing such phenomena as quantum capacitance and negative capacitance. By the formation of magnetically active nano-centers through which it was possible to achieve the conditions of resonance tunneling, which as a consequence leads to the creation of EMF under normal conditions and under the influence of a constant magnetic field. This biintercalant clathrate acquires practical appeal for the manufacture of high-Q radio-frequency capacitors in terms of anomalous increase in dielectric constant in the megahertz range (εmax ≈ 5.5·104), simultaneously accepting the value of the dielectric loss tangent less than 1. At the same time, it also shows a negative magneto-capacitive effect was also obtained, which can be used for the construction of highly sensitive magnetic field sensors of capacitive type. Due to the ferroelectric guest component, this clathrate exhibits charge storage properties that can be used to create non-volatile memory so-called memristors. [ABSTRACT FROM AUTHOR]

The most prominent theoretical question for high-temperature superconductors is, "Why is Tc so much higher in these materials than in conventional metallic superconductors?" My answer is that the dopants (often, but not always, oxygen vacancies or interstitials) have formed self-organized percolative networks to screen the strong ionic fields in and between tetragonal layers. This model fits very well to Geballe's latest data with Tc = 84 K on apparently overdoped Mo-YBCO sol-gel samples, showing the effectiveness of self-organization. [ABSTRACT FROM AUTHOR]

The coexistence of electric dipoles and itinerant electrons in a solid was postulated decades ago, before being experimentally established in several 'polar metals' during the last decade. Here, we report a concentration-driven polar-to-nonpolar phase transition in electron-doped BaTiO3. Comparing our case with other polar metals, we find a particular threshold concentration (n*) linked to the dipole density (nd). The universal ratio n d n * ≈ 8.0 (6) suggests a common mechanism across different polar systems, possibly explained by a dipolar Ruderman-Kittel-Kasuya-Yosida theory. Moreover, in BaTiO3, we observe enhanced thermopower and upturn on resistivity at low temperatures near n*, resembling the Kondo effect. We argue that local electric dipoles act as two-level-systems, whose fluctuations couple with surrounding electron clouds, giving rise to a potential dipolar-counterpart of the Kondo effect. Our findings unveil a mostly uncharted territory for exploring emerging physics associated with electron-dipole correlations, encouraging further theoretical work on dipolar-RKKY and Kondo interactions. [ABSTRACT FROM AUTHOR]

Context: Oxygen is a chemically active gas. Metal uranium will be rapidly oxidized when exposed to oxygen directly, forming a complex and uncompacted oxide layer on the surface. The U–O2 reaction system is a very complex metal oxidation system. The surface oxidation reaction of uranium-niobium alloy is more complex, and it is also the main corrosion form of uranium-niobium alloy. Exploring the microscopic mechanism of surface oxidation corrosion of uranium-niobium alloy is of great significance for understanding the surface corrosion phenomenon in practical applications. The adsorption of O2 on U–Nb (5at.%) surface was investigated by first-principles calculation using a periodic slab model within the density functional theory (DFT). The effect of different levels of Nb doping on O adsorption was investigated, and the stability of O–U and O–Nb adsorption was studied in conjunction with the Bader charge distribution, differential charge density map, electron density of states, and surface work function. The results showed that physical adsorption happens when O2 is vertically adsorbed at the top site of Nb atom, whereas dissociative adsorption happened in all other configurations considered here. The interaction between adsorbed O2 and U–Nb surface was essentially the hybridization between the O/2p orbital electrons and the U/6d, U/5f, Nb/4p, Nb/5s, and Nb/4d orbital electrons to form a relatively stable ionic bond. When Nb was doped into the second layer of the surface, the most stable O2 adsorption configuration was top-site horizontal adsorption. The adsorption energy was − 22.38 eV, which was more negative than the adsorption energy of − 21.38 eV for the first doped layer horizontal adsorption at hollow-site. The interaction was essentially the hybridization between O/2p orbital electrons and U/6d and U/5f electrons and between O/2s orbital electrons and U/6p orbital electrons to form a relatively stable ionic bond. Method: In this paper, the adsorption and dissociation of oxygen molecules on the surface of U–Nb system were systematically studied by first-principles calculations, in order to explore the surface oxidation corrosion mechanism of uranium-niobium alloy from the micro level. The VASP program uses PAW pseudopotential, which belongs to the density functional method, and uses DSP. [ABSTRACT FROM AUTHOR]

The phonon-drag effect is useful for improving the thermoelectric performance, especially the Seebeck coefficient. Therefore, the phonon and electron transport properties of Si single crystals at different carrier densities were investigated, and the relationship between these properties and the phonon-drag effect was clarified. Phonon transport properties were determined using nanoindentation and spot-periodic heating radiation thermometry. The electron transport properties were determined based on the electrical conductivity of Si. The diffusive Seebeck coefficient derived from the electron transport properties was in good agreement with previous reports. However, the value of the phonon-drag Seebeck coefficient derived from the phonon transport properties is very low. This phenomenon suggests that phonons with a normal mean free path (MFP) do not contribute to the increase in the Seebeck coefficient; however, phonons with a long MFP and low frequency increase the Seebeck coefficient via the phonon-drag effect. Moreover, the phonon-drag effect was sufficiently pronounced even at 300 K and in the heavily doped region. These features are key in designing thermoelectric materials with enhanced performance derived from the phonon-drag effect. [ABSTRACT FROM AUTHOR]

Interests in organic quantum materials (OQMs) have been explosively growing in the field of condensed physics of matter due to their rich chemistry and unique quantum properties. They are strongly correlated systems and show novel electromagnetic performance such as high‐temperature superconducting, quantum sensing, spin electronics, quantum dots, topological insulating, quantum Hall effects, spin liquids, qubits, and so forth, which exhibit promising prospects in information communication and thus facilitate the construction of a modern intelligent society. This article reviews recent developments in the research on the electromagnetic characteristics of OQMs. We mainly give an overview on the progress of superconductors and quantum spin liquids based on organic materials and describe their possible mechanisms. Numerous experimental findings exhibit new exciton interactions and provide insights into exotic electronic properties. Finally, their association and strategies for realizing multiple quantum states in one system are discussed. [ABSTRACT FROM AUTHOR]

In this study, we reported the DC magnetic measurement M(H) loops, intragrain critical current density (Jc), pinning mechanisms, and thermal fluctuations induced excess conductivity for polycrystalline products of YBa2Cu3O7-δ (Y123) with and without PbO addition. Pristine Y123 and PbO-added Y123 samples were produced by considering the solid-state reaction process. The produced products were surveyed using X-ray diffraction (XRD), scanning, and transmission electron microscopes (SEM and TEM) along with energy-dispersive X-ray (EDX) spectroscopy, magnetization hysteresis loops, and electrical resistivity measurements. The combination of PbO with the Y123 polycrystalline preserved the YBa2Cu3O7-δ orthorhombic structure, and amplified Jc under an external magnetic field, thereby changing the flux pinning ability. Excess conductivity analysis was performed near the critical temperature using the Aslamazov–Larkin model. It was established that PbO upgrades the superconducting parameters estimated at a temperature of 0 K, viz. the critical current density ( J c 0 ), the upper and lower critical magnetic fields B c 1 0 and B c 2 0 , respectively. [ABSTRACT FROM AUTHOR]