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Uniquely, large-bipolarons' self-trapped holes occupy superoxygens, each comprising four oxygens circumscribed by four coppers in a CuO2 plane, formed as oxygens relax inward and coppers relax outward. Critically, concomitant oxygen-to-copper electron transfer eliminates copper spins. The d-symmetry of superoxygens' ground state molecular orbital tracks the superoxygens' predominant zero-point radial vibrations. These large bipolarons' distinctive charge transport, absorption, magnetism, local atomic vibrations, condensation into a liquid, and subsequent superconductivity are consistent with cuprate superconductors' long-established unusual properties. [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]

The enigmatic mechanism underlying unconventional high-temperature superconductivity, especially the role of lattice dynamics, has remained a subject of debate. Theoretical insights have long been hindered due to the lack of an accurate first-principles description of the lattice dynamics of cuprates. Recently, using the r2SCAN meta-generalized gradient approximation (meta-GGA) functional, we have been able to achieve accurate phonon spectra of an insulating cuprate YBa2Cu3O6 and discover significant magnetoelastic coupling in experimentally interesting Cu–O bond stretching optical modes [Ning et al., Phys. Rev. B 107, 045126 (2023)]. We extend this work by comparing Perdew–Burke–Ernzerhof and r2SCAN performances with corrections from the on-site Hubbard U and the D4 van der Waals (vdW) methods, aiming at further understanding on both the materials science side and the density functional side. We demonstrate the importance of vdW and self-interaction corrections for accurate first-principles YBa2Cu3O6 lattice dynamics. Since r2SCAN by itself partially accounts for these effects, the good performance of r2SCAN is now more fully explained. In addition, the performances of the Tao–Mo series of meta-GGAs, which are constructed in a different way from the strongly constrained and appropriately normed (SCAN) meta-GGA and its revised version r2SCAN, are also compared and discussed. [ABSTRACT FROM AUTHOR]

The enigmatic mechanism underlying unconventional high-temperature superconductivity, especially the role of lattice dynamics, has remained a subject of debate. Theoretical insights have long been hindered due to the lack of an accurate first-principles description of the lattice dynamics of cuprates. Recently, using the r2SCAN meta-generalized gradient approximation (meta-GGA) functional, we have been able to achieve accurate phonon spectra of an insulating cuprate YBa2Cu3O6 and discover significant magnetoelastic coupling in experimentally interesting Cu–O bond stretching optical modes [Ning et al., Phys. Rev. B 107, 045126 (2023)]. We extend this work by comparing Perdew–Burke–Ernzerhof and r2SCAN performances with corrections from the on-site Hubbard U and the D4 van der Waals (vdW) methods, aiming at further understanding on both the materials science side and the density functional side. We demonstrate the importance of vdW and self-interaction corrections for accurate first-principles YBa2Cu3O6 lattice dynamics. Since r2SCAN by itself partially accounts for these effects, the good performance of r2SCAN is now more fully explained. In addition, the performances of the Tao–Mo series of meta-GGAs, which are constructed in a different way from the strongly constrained and appropriately normed (SCAN) meta-GGA and its revised version r2SCAN, are also compared and discussed. [ABSTRACT FROM AUTHOR]

The X2MH6 family, consisting of an electropositive cation Xn+ and a main group metal M octahedrally coordinated by hydrogen, have been identified as promising templates for high‐temperature conventional superconductivity. Herein, we analyze the electronic structure of two members of this family, Mg2IrH6 and Ca2IrH6, showing why the former may possess superconducting properties rivaling those of the cuprates, whereas the latter does not. Within Mg2IrH6 the vibrations of the anions IrH64− anions are key for the superconducting mechanism, and they induce coupling in the eg* ${e_g^{\ast} }$ set of orbitals, which are antibonding between the H 1s and the Ir dx2-y2 ${d_{x^2 - y^2 } }$ or dz2 ${d_{z^2 } }$ orbitals. Because calcium possesses low‐lying d‐orbitals, eg* ${e_g^{\ast} }$ →Ca d back‐donation is preferred, quenching the superconductivity. Our analysis explains why high critical temperatures were only predicted for second or third row X metal atoms, and may provide rules for identifying likely high‐temperature superconductors in other systems where the antibonding anionic states are filled. [ABSTRACT FROM AUTHOR]

The magnetic excitation spectrum of most high-temperature superconducting (HTSC) cuprates is hour-glass shaped. The observation of hour-glass spectra in the isostructural Sr-doped cobaltates La2−xSrxCoO4 gives rise to a deeper understanding of these spectra. So far, hour-glass spectra have been only observed in those systems that evolve from incommensurate magnetic peaks. Here, we report on the appearance of hour-glass spectra in oxygen-doped cobaltates La2CoO4+δ. The high-energy part of the hour-glass spectrum of oxygen doped cobaltates is extremely anisotropic with a very prominent stripe-like appearance not seen that clearly in purely Sr-doped compounds. A charge stripe scenario is evidenced by (polarized) neutron diffraction measurements and also corroborated by spin wave simulations. Our results indicate that charge stripes are the origin of the anisotropic stripe- or diamond-shaped high-energy part of the hour-glass spectrum. A link between hour-glass spectra and charge stripes could be of relevance for the physics in HTSC cuprates. The hour-glass magnetic excitation spectrum is a universal feature of most cuprate high-temperature superconductors, yet the exact origins are still debated. Here, using inelastic neutron scattering techniques, the authors report hour-glass magnetic spectra in an oxygen-doped cobaltate La2CoO4+δ and discuss the potential link with charge stripes and the "diamond-shaped" high energy part of the hour-glass spectrum of this system. [ABSTRACT FROM AUTHOR]

In unconventional superconductors, coupled charge and lattice degrees of freedom can manifest in ordered phases of matter that are intertwined. In the cuprate family, fluctuating short-range charge correlations can coalesce into a longer-range charge density wave (CDW) order which is thought to intertwine with superconductivity, yet the nature of the interaction is still poorly understood. Here, by measuring subtle lattice fluctuations in underdoped YBa2Cu3O6+y on quasi-static timescales (thousands of seconds) through X-ray photon correlation spectroscopy, we report sensitivity to both superconductivity and CDW. The atomic lattice shows remarkably faster relaxational dynamics upon approaching the superconducting transition at Tc ≈ 65 K. By tracking the momentum dependence, we show that the intermediate scattering function almost monotonically scales with the relaxation distance of atoms away from their average positions above Tc and in the presence of the CDW state, while this peculiar trend is reversed for other temperatures. These observations are consistent with an incipient CDW stabilized by local strain. This work provides insights into the crucial role of relaxational atomic fluctuations for understanding the electronic physics cuprates, which are inherently disordered due to carrier doping. [ABSTRACT FROM AUTHOR]

The high-temperature superconducting cuprates host unidirectional spin- and charge-density-wave orders that can intertwine with superconductivity in nontrivial ways. While the charge components of these stripes have now been observed in nearly all cuprate families, their detailed evolution with doping varies across different materials and at high and low temperatures. We address this problem using nonperturbative determinant quantum Monte Carlo calculations for the three-band Hubbard model. Using an efficient implementation, we can resolve the model's fluctuating spin and charge modulations and map their evolution as a function of the charge transfer energy and doping. We find that the incommensurability of the charge modulations is decoupled from the spin modulations and decreases with hole doping, consistent with experimental measurements at high temperatures. These findings support the proposal that the high-temperature charge correlations are distinct from the intertwined stripe order observed at low-temperature and in the single-band Hubbard model. [ABSTRACT FROM AUTHOR]

Superconductivity had been one of the most enigmatic phenomena in condensed matter physics, puzzling the best theorists for 45 years, since the original discovery by Kamerlingh-Onnes in 1911 till the final solution by Bardeen, Cooper, and Schrieffer (BCS) in 1957. The original BCS proposal assumed the highest-symmetry form for the superconducting order parameter Δ, namely, a constant, and a uniform pairing interaction due to attractive mediation of ionic vibration. While it was rather soon realized that generalizations onto k-dependent order parameters and anisotropic pairing interaction was straightforward, only thirty years later, upon the discovery of high-temperature superconductivity in cuprates, high-order angular dependence of Δ and repulsive interaction, mediated by spin fluctuations or Coulomb repulsion brought such "unconventional" into the spotlight. In 2008 yet another such system was discovered, and eventually the idea of repulsion-mediated unconventional superconductivity was generally accepted. Apart from the two specific systems mentioned above, a large number of various specific implementations of this idea have been proposed, and it is becoming increasingly clear that it is worth studying mathematically how unconventional superconductivity emerges, and with what properties, for a simple, but sufficiently general theoretical model. In our project, we study systematically unconventional superconductivity in an isotropic two-dimensional model system of electrons, subjected to repulsive interactions of a simple, but physically motivated form: a delta function peaked at a particular momentum (from 0 to twice the Fermi momentum), or Gaussian of varying widths. [ABSTRACT FROM AUTHOR]

In a recent paper [B. Michon et al., Nat. Commun. (2023) 14:3033], optical conductivity experiments in cuprate superconductors were shown to display scaling properties consistent with the Marginal Fermi Liquid theory. Here, we argue that the temperature regime studied in these experiments does not allow for distinguishing between Marginal Fermi Liquid and Shrinking Fermi Liquid. In the latter scenario, which we recently proposed and which applies near a quantum critical point, dynamical fluctuations of the order parameter with a short correlation length mediate a nearly isotropic scattering among the quasiparticles over the entire Fermi surface leading to strange metal behavior. If the damping of these nearly local fluctuations increases by decreasing the temperature, the Fermi liquid regime shrinks and the strange metal behavior is extended to the lowest temperatures. This Shrinking Fermi Liquid scenario has many similarities and some differences with respect to the Marginal Fermi Liquid theory. In particular, we show that the approximate scaling properties of the optical conductivity in some high-frequency regimes predicted by the Shrinking Fermi Liquid scenario account for a very good description of the experimental data. [ABSTRACT FROM AUTHOR]

The long-term (more than 20 years) aging effect and degradation study of a Y 1 - x Ca x SrBaCu 2.80 BO 3 0.20 O y powder ceramic superconductors with 0.10 ≤ x ≤ 0.50 are studied by X-ray diffraction and DC Magnetic Property Measurement System (DC-MPMS-SQUID). The samples prepared by solid state reaction were well characterized and stored at normal conditions of pressure and temperature for more than 20 years. The aged samples present the formation of BaCO3 due to the exposure with the environment during that period. The temperature dependence of the magnetization under Hext = 10 Oe reveal that the superconducting state remains in the samples, except for that with x = 0.10, where a higher magnetic field (20 kOe) is required to be applied to observe a superconducting response. Remarkably, the samples show the same TC values despite the aging indicating that the magnetic alignment of the formed BaCO3 affects the magnetic propertied of the whole sample but not the superconducting alignment of the doped YBCO. This is also reflected in the χ - 1 (T) plots at normal state, which show both ferromagnetic and antiferromagnetic contribution, in contrast to what was obtained in the pristine samples which only presented antiferromagnetic coupling. From M(H) loops, the critical current density values at 10 K are obtained by using the critical Bean model in order to estimate the transport capabilities of the aged powders. [ABSTRACT FROM AUTHOR]

Charge order has been a central focus in the study of cuprate high-temperature superconductors due to its intriguing yet not fully understood connection to superconductivity. Recent advances in resonant inelastic x-ray scattering (RIXS) in the soft x-ray regime have enabled the first momentum-resolved studies of dynamic charge order correlations in the cuprates. This progress has opened a window for a more nuanced investigation into the mechanisms behind the formation of charge order (CO) correlations. This review provides an overview of RIXS-based measurements of dynamic CO correlations in various cuprate materials. It specifically focuses on electron-doped cuprates and Bi-based hole-doped cuprates, where the CO-related RIXS signals may reveal signatures of the effective Coulomb interactions. This aims to explore a connection between two central phenomena in the cuprates: strong Coulomb correlations and CO-forming tendencies. Finally, we discuss current open questions and potential directions for future RIXS studies as the technique continues to improve and mature, along with other probes of dynamic correlations that would provide a more comprehensive picture. [ABSTRACT FROM AUTHOR]

The attractive interaction in conventional BCS superconductors is provided by a bosonic mode. However, the pairing glue of most unconventional superconductors is unknown. The effect of electron-boson coupling is therefore extensively studied in these materials. A key signature is dispersion kinks that can be observed in the spectral function as abrupt changes in velocity and lifetime of quasiparticles. Here, we show the existence of two kinks in the unconventional iron-based superconductor RbFe2As2 using angle-resolved photoemission spectroscopy (ARPES) and dynamical mean field theory (DMFT). In addition, we observe the formation of a Hubbard band multiplet due to the combination of Coulomb interaction and Hund's rule coupling in this multiorbital system. We demonstrate that the two dispersion kinks are a consequence of these strong many-body interactions. This interpretation is in line with a growing number of theoretical predictions for kinks in various general models of correlated materials. Our results provide a unifying link between iron-based superconductors and different classes of correlated, unconventional superconductors such as cuprates and heavy-fermion materials. Abrupt changes, or kinks, in electron dispersion, caused by the coupling of electronic excitations to collective modes, could provide insights into the superconducting pairing mechanism. Here the authors report dispersion kinks driven by electronic correlations in the normal state of an iron-based superconductor. [ABSTRACT FROM AUTHOR]

Ever since the discovery of high-temperature superconductivity in cuprates, gaining microscopic insights into the nature of pairing in strongly correlated systems has remained one of the greatest challenges in modern condensed matter physics. Following recent experiments reporting superconductivity in the bilayer nickelate La3Ni2O7 (LNO) with remarkably high critical temperatures of Tc = 80 K, it has been argued that the low-energy physics of LNO can be described by the strongly correlated, mixed-dimensional bilayer t–J model. Here we investigate this bilayer system and utilize density matrix renormalization group techniques to establish a thorough understanding of the model and the magnetically induced pairing through comparison to the perturbative limit of dominating inter-layer spin couplings. In particular, this allows us to explain appearing finite-size effects, firmly establishing the existence of long-range superconducting order in the thermodynamic limit. By analyzing binding energies, we predict a BEC–BCS crossover as a function of the Hamiltonian parameters. We find large binding energies of the order of the inter-layer coupling that suggest strikingly high critical temperatures of the Berezinskii–Kosterlitz–Thouless transition, raising the question of whether (mixD) bilayer superconductors possibly facilitate critical temperatures above room temperature. The authors study a minimal model to describe the physics of bilayer nickelates, a novel high-temperature superconductor. They find that the model features extraordinarily high critical temperatures for superconductivity, and gain a detailed understanding of the underlying physics through an intuitive perturbative limit. [ABSTRACT FROM AUTHOR]

In this work, we derive equations for the superconducting nematic order parameter, critical temperature, and chemical potential for two-dimensional rectangular lattice by taking into account nearest- and next-nearest-neighbor hopping of carriers (electrons or holes). By solving the obtained equations, we have found that the symmetry of the order parameter and other superconducting properties strongly depend on the sign and the magnitude of the next-nearest neighbor hopping and on doping. We have analyzed the possible crossover of the system from the Bose–Einstein condensation to the Bardeen–Cooper–Schrieffer superconductivity regimes with increasing the electron density. As we show, the crossover, which can be tuned by both doping and nearest neighbor hopping, only occurs in the s-channel at physically meaningful values of these parameters. A possible connection of the obtained results to the properties of doped high-temperature cuprate superconductors is discussed. [ABSTRACT FROM AUTHOR]

The validity of a new alternative (Bose-liquid) approach, which has advantage over the Fermi-liquid (BCS-like) approach, to unconventional superconductivity in organic and high-Tc cuprate superconductors is consi-dered. The results of a detailed study of the temperature dependence of the magnetic field penetration depth in these materials are presented. It is argued that organic materials and doped high-Tc cuprates can be considered as bosonic superconductors in which tightly-bound (polaronic) Cooper pairs behave as bosons like 4He atoms and condense into two distinct Bose superfluids below the superconducting transition temperature Tc. It is shown that unconventional (Bose-liquid) superconductivity in organic compounds and doped cuprates arises as a result of pair and single particle condensations of attracting bosons into two Bose superfluids below two characteristic temperatures Tc (temperature of onset of superconducting transition or pair condensation of attracting bosons) and T c ∗ (temperature of onset of single particle condensation of attracting bosons). The existing experimental data on the temperature dependence of the London penetration depth λ L (T) in organic and high-Tc cuprate superconductors are analysed in terms of the theory of three-dimensional (3D) Bose-liquid superconductivity. By comparing the predictions of this theory for temperature dependences λ L (T) with measured temperature dependences λ L (T) in the organic superconductor k-(BEDT–TTF)2Cu(NCS)2 and the high-Tc cuprate superconductors YBa2Cu3O7–δ, YBa2Cu3O9–δ (δ = 2.1 ± 0.05) and YBa2Cu3O6.95 found that the temperature dependences of the new superconducting order parameter and the magnetic field penetration depth in these superconductors are anomalous and show a pronounced kink (or bend) near the characteristic temperature T c ∗ lower than Tc. The existence of two different (so-called gapped and gapless) regimes of 3D Bose-liquid superconductivity in the studied organic and high-Tc cuprate superconductors in two temperature ranges T c ∗ < T < T c and 0 ≤ T ≤ T c ∗ is predicted. The validity of the following laws in unconventional (bosonic) superconductors is proved: the exponential temperature dependence of λ L (T) at temperatures above T c ∗ is a consequence of the appearance of the energy gap in the excitation spectrum of a 3D superfluid Bose liquid, and the power-law temperature dependence of λ L (T) at low temperatures below T c ∗ down to T = 0 is a direct consequence of the disappearance of the energy gap in the excitation of a 3D superfluid Bose liquid at T ≤ T c ∗. Our theoretical results for the low- and high-temperature dependences of λ L (T) / λ L (0) and λ L 2 (0) / λ L 2 (T) are in good quantitative agreement with experimental results in organic and high-Tc cuprate superconductors. It is found that the superconductivity in these materials is essentially three-dimensional in nature and is well described by the theory of two different Bose superfluids. [ABSTRACT FROM AUTHOR]

Propagation of spin-singlet Cooper pairs from a conventional superconductor into a ferromagnetic material over comparatively long distances was explained by the emergence at their interface of equal-spin triplet pairing that is no longer subject to pair-breaking mechanisms within magnetic counterparts. This phenomenon is produced by interfacial magnetic inhomogeneity and most spectacularly manifests itself in all-oxide heterostructures involving cuprates and manganites. In contrast to previous works, mostly devoted to bilayers of these materials, we are studying the long-penetration effect in random binary nanocomposites formed by half-metallic La2/3Ca1/3MnO3 nanoparticles and micro-sized particles of a d-wave superconductor Bi2Sr2Ca2Cu3Oy. With point-contact spectro-scopy, we revealed the presence of two superconducting gaps, namely the gap Δd in the cuprate granules partly suppressed due to the proximity effect and the proximity-induced gap in the spectrum of excitations of equal-spin triplet Cooper pairs. External magnetic fields, which tend to align the magnetizations at and near the interfaces, significantly suppressed the features of the superconducting origin including a symmetrical periodic structure at energies less than the energy Δd, while the conductivity in the normal state changes only slightly. Like related oxide bilayers, it enables control of the supercurrent transfer across hybrid nanocomposite super-spintronic devices by tuning the degree of magnetic inhomogeneity. [ABSTRACT FROM AUTHOR]

Research of infinite-layer nickelates has unveiled a broken translation symmetry, which has sparked significant interest in its root, its relationship to superconductivity, and its comparison to charge order in cuprates. In this study, resonant x-ray scattering measurements were performed on thin films of infinite-layer PrNiO2+ δ . The results show significant differences in the superlattice reflection at the Ni L 3 absorption edge compared to that at the Pr M 5 resonance in their dependence on energy, temperature, and local symmetry. These differences point to two distinct charge orders, although they share the same in-plane wavevectors. It is suggested that these dissimilarities could be linked to the excess oxygen dopants, given that the resonant reflections were observed in an incompletely reduced PrNiO2+ δ film. Furthermore, azimuthal analysis indicates that the oxygen ligands likely play a crucial role in the charge modulation revealed at the Ni L 3 resonance. [ABSTRACT FROM AUTHOR]

The highest ambient‐pressure Tc among binary compounds is 40 K (MgB2). Higher Tc is achieved in high‐pressure hydrides or multielement cuprates. Alternatively, are explored superconducting properties of binary, metastable sub‐oxides, that may emerge under extremely low oxygen partial pressure. The emphasis is on the rock‐salt structure, which is known to promote superconductivity, and exploring AlO, ScO, TiO, and NbO. Dynamic lattice stability is achieved by introducing metal and oxygen vacancies in the fashion of Nb1−xO1−x‐type structure (x = ¼). The electron‐phonon (e‐ph) coupling is remarkably large in Al1−xO1−x and Ti1−xO1−x (λ ≈ 2 at x = ¼), with Tc ≈ 35 K according to the Allen–Dynes equation. Significantly, the coupling strength is comparable to that in high‐pressure hydrides, yet, in contrast to hydrides and MgB2, the coupling is largely driven by low frequency phonons. Sc1−xO1−x and Nb1−xO1−x show significantly smaller λ and Tc. Further, hydrogen intercalation to boost λ and Tc is investigated. Only Ti1−x(O1−xHx) and Nb1−x(O1−xHx) are dynamically stable upon intercalation, where H, respectively, decreases and increases Tc. The effect of H doping on electronic structure and Tc is discussed. Altogether, the study suggests that metal sub‐oxides are promising compounds to achieve strong e‐ph coupling at ambient pressure. [ABSTRACT FROM AUTHOR]

Cd2+ cation doped CsPbCl3 single crystals were synthesized, and their luminescent properties were investigated under excitation with synchrotron radiation quanta with energy greater than Eg and at a sample temperature of 12 K. Pure single crystals exhibit a narrow band of exciton emission at 416.7 nm. Doping the single crystals leads to a high-energy shift of the excitonic luminescence, the appearance of new luminescent bands, the broadening of the luminescent bands, an increase in the decay time constants, and a significant enhancement of the luminescence intensity. The observed changes in luminescent parameters upon doping are discussed in terms of the crystal structure ordering, a decrease in the number of defects responsible for capturing charge carriers at the stage of electronic excitation thermalization, and a decrease in defects that quench excitonic luminescence. Doped single crystals with decay times of the order of 0.4 ns and intensities that significantly exceed the intensity of pure single crystals can be promising scintillation materials for positron emission tomography in the time-of-flight mode. [ABSTRACT FROM AUTHOR]

GdI 2 monolayer is a promising material for spintronics applications due to its robust room-temperature ferromagnetism and sizable valley polarization. In two-dimensional van der Waals magnets, interlayer magnetic coupling plays a crucial role in device applications. The performance of these devices can be effectively tuned by adjusting the stacking order, charge doping, and strain. By performing first-principles calculations, we have demonstrated that the interlayer magnetic coupling in bilayer GdI 2 is highly dependent on the stacking order, which can be tuned between ferromagnetic (FM) and antiferromagnetic orders through lateral shifting. Furthermore, the interlayer magnetic coupling can also be tuned by charge doping and strain, where both electron and hole doping can enhance the FM coupling interaction between layers, and the interlayer FM coupling can be strengthened with increasing biaxial tensile strain. These results show that bilayer GdI 2 has rich tunable interlayer magnetic interactions, which can be used in designing interesting spin tunnel field-effect transistor devices. [ABSTRACT FROM AUTHOR]

GdI 2 monolayer is a promising material for spintronics applications due to its robust room-temperature ferromagnetism and sizable valley polarization. In two-dimensional van der Waals magnets, interlayer magnetic coupling plays a crucial role in device applications. The performance of these devices can be effectively tuned by adjusting the stacking order, charge doping, and strain. By performing first-principles calculations, we have demonstrated that the interlayer magnetic coupling in bilayer GdI 2 is highly dependent on the stacking order, which can be tuned between ferromagnetic (FM) and antiferromagnetic orders through lateral shifting. Furthermore, the interlayer magnetic coupling can also be tuned by charge doping and strain, where both electron and hole doping can enhance the FM coupling interaction between layers, and the interlayer FM coupling can be strengthened with increasing biaxial tensile strain. These results show that bilayer GdI 2 has rich tunable interlayer magnetic interactions, which can be used in designing interesting spin tunnel field-effect transistor devices. [ABSTRACT FROM AUTHOR]

The connection between the long-range antiferromagnetic order in cuprates and the high-temperature superconductivity is a scientific problem that has yet to be solved after nearly four decades. The properties and difficulties of describing nickelate superconductors are similar to those of cuprates. Recently, Fowlie et al. [Nat. Phys. 18, 1043 (2022)] aimed to detect the antiferromagnetic order in R1−xSrxNiO2 (R = Nd, Pr, La; x ∼ 0, 0.2) films by using the muon spin rotation (μSR) technique. The research group reported the presence of short-range antiferromagnetic order in every nickelate studied. Here, our goal was to prove that this interaction is present in the nickelate films. We did this by analyzing the temperature dependent resistivity, ρ(T), data from the research group. Global ρ(T) data fits to the advanced Bloch–Grüneisen model showed that each of the R1−xSrxNiO2 compounds can be characterized by a unique power-law exponent, p (where p = 2 for the electron–electron scattering, p = 3 for the electron–magnon scattering, and p = 5 for the electron–phonon scattering), and global characteristic temperature, Tω (which has the meaning of the Debye temperature at p = 5). We found that p = 2.0 in Nd- and Pr-based compounds and p = 1.3 for La-based compounds. The latter value does not have any interpretation within established theoretical models. We also analyzed ρ(T) data for Nd1–xSrxNiO2 (0.125 ≤ x ≤ 0.325) reported by Lee et al. [Nature 619, 288 (2023)]. Our analysis of nickelates led us to conclude that a new theoretical model is needed to describe ρ(T) in materials exhibiting a short-range antiferromagnetic order. [ABSTRACT FROM AUTHOR]

SmNiO 3 is a representative quantum material exhibiting the antidoping behavior, where the conductivity of the material is reduced rather than increased by electron doping. Recent experimental and theoretical works have demonstrated a phase transition of SmNiO 3 with large conductance changes via chemical methods. However, the effect of electron doping via interfacial charge transfer in SmNiO 3 is much less studied. In this work, the first-principles density functional theory (DFT)+ U method is employed to investigate the SmNiO 3 /YTiO 3 superlattice, in which the YTiO 3 layer acts as the electron donor. Compared with the chemical doping in SmNiO 3 , several interesting physical phenomena have been predicted in SmNiO 3 /YTiO 3 superlattices due to the lattice and electronic reconstructions. First, at a doping concentration of 1 e − per Ni, i.e., (SmNiO 3) 1 /(YTiO 3) 1 superlattice, all Ni 3 + are converted to Ni 2 + , resulting in a Mott-insulating phase, similar to the chemical doping in the pristine material. Interestingly, such a Mott gap can be efficiently modulated by tuning the stacking orientation. Second, at a doping concentration of 1 2 e − per Ni, i.e., [ 001 ]-orientated (SmNiO 3) 2 /(YTiO 3) 1 superlattice, the electronic structure associated with charge ordering depends on the concrete magnetic order, giving rise to magnetism-dependent electronic behavior. In addition, as the doping concentration further decreases (i.e., a doping concentration of 1 3 e − /Ni), a metallic state is predicted in a [ 001 ]-orientated (SmNiO 3) 3 /(YTiO 3) 1 superlattice, which is quite different from the case of chemical doping. [ABSTRACT FROM AUTHOR]

The anomalous strange metal phase found in high-Tc cuprates does not follow the conventional condensed-matter principles enshrined in the Fermi liquid and presents a great challenge for theory. Highly precise experimental determination of the electronic self-energy can provide a test bed for theoretical models of strange metals, and angle-resolved photoemission can provide this as a function of frequency, momentum, temperature and doping. Here we show that constant energy cuts through the nodal spectral function in (Pb,Bi)2Sr2−xLaxCuO6+δ have a non-Lorentzian lineshape, consistent with a self-energy that is k dependent. This provides a new test for aspiring theories. Here we show that the experimental data are captured remarkably well by a power law with a k-dependent scaling exponent smoothly evolving with doping, a description that emerges naturally from anti-de Sitter/conformal-field-theory based semi-holography. This puts a spotlight on holographic methods for the quantitative modelling of strongly interacting quantum materials like the cuprate strange metals. Strange metal behaviour of high-Tc superconductors, characterised by unconventional electrical and thermodynamic properties, still poses challenges for theory. Smit et al. report experimental features in the self-energy of a strange metal that are consistent with predictions by holographic theoretical methods. [ABSTRACT FROM AUTHOR]

Hyperspectral imaging techniques have a unique ability to probe the inhomogeneity of material properties whether driven by compositional variation or other forms of phase segregation. In the doped cuprates, iridates, and related materials, scanning tunneling microscopy/spectroscopy (STM/STS) measurements have found the emergence of pseudogap "puddles" from the macroscopically Mott insulating phase with increased doping. However, categorizing this hyperspectral data by electronic order is not trivial and has often been done with ad hoc methods. In this paper, we demonstrate the utility of k-means, a simple and easy-to-use unsupervised clustering method, as a tool for classifying heterogeneous scanning tunneling spectroscopy data by electronic order for Rh-doped Sr2IrO4, a cuprate-like material. Applied to STM data acquired within the Mott phase, k-means was able to identify areas of Mott order and of pseudogap order. The unsupervised nature of k-means limits avenues for bias and provides clustered spectral shapes without a priori knowledge of the physics. Additionally, we demonstrate the use of k-means as a preprocessing tool to constrain phenomenological function fitting. Clustering the data allows us to reduce the fitting parameter space, limiting over-fitting. We suggest k-means as a fast, simple model for processing hyperspectral data on materials of mixed electronic order. [ABSTRACT FROM AUTHOR]

In cuprates, the superconducting transition temperature (Tc) is closely related to the number n of CuO2 planes per unit cell. The studies on multi‐layered cuprates offer insights into the physical properties and pairing mechanisms of superconductivity. However, the synthesis and stability of ultra‐multilayered cuprates pose significant challenges. Here, a newly discovered seven‐layered cuprate CuBa2Ca6Cu7O17±δ grown under high pressure is reported. Magnetization and transport measurements confirm bulk superconductivity with Tc of ≈85 K. The magnetization hysteresis loops, critical current density (Jc), and irreversibility fields of CuBa2Ca6Cu7O17±δ are also investigated. The novel compound CuBa2Ca6Cu7O17±δ provides an ideal platform for studying the physics of multi‐layered cuprates. [ABSTRACT FROM AUTHOR]

In recent years, the electronic structures of organocuprates in general and the complex [Cu(CF3)4]− in particular have attracted significant interest. A possible key indicator in this context is the reactivity of these species. Nonetheless, this aspect has received only limited attention. Here, we systematically study the series of tetra‐alkyl cuprates [MenCu(CF3)4−n]− and their unimolecular reactivity in the gas phase, which includes concerted formal reductive eliminations as well as radical losses. Through computational studies, we characterize the electronic structures of the complexes and show how these are connected to their reactivity. We find that all [MenCu(CF3)4−n]− ions feature inverted ligand fields and that the distinct reactivity patterns of the individual complexes arise from the interplay of different effects. [ABSTRACT FROM AUTHOR]

We study the transport properties of underdoped trilayer cuprate HgBa2Ca2Cu3O8+δ with doping level p = 0.10–0.12 in magnetic field up to 88 T. We report for the first time in a cuprate superconductor a dramatic change of the quantum oscillation spectrum versus temperature, which is accompanied by a sign change of the Hall effect below T ≈10 K. Based on numerical simulations, we infer a Fermi surface reconstruction in the inner plane from an antiferromagnetic state (hole pockets) to a biaxial charge density wave state (electron pockets). We show that both orders compete and share the same hotspots of the Fermi surface, and we discuss our result in the context of spin-fermion models. [ABSTRACT FROM AUTHOR]

Yttrium barium copper oxide (YBCO) is used for special applications in linear generators because of its excitation loss, lower weight, and higher efficiency. These qualities enable the compound to operate better than the conventional copper wire coil in the stator unit of the linear generator. However, the continuous use of YBCO in linear generators has a fundamental challenge that affects industrial production and material stability after prolonged use. This paper seeks to sustain the adoption of YBCO by improving its quality for linear generator applications. The yttrium cuprates modification (YBYbCO) was synthesized using the solid-state reaction technique by doping YBCO with ytterbium. The crystalline structure, microstructural pattern, and stability of the new sample were adequately measured and found to be structurally stable to ensure durability. It was reported that applying YBYbCO in the linear generator would lead to a 200% increase in energy generation. The higher number of particles and lower individual particulate resistance enable it to withstand chemical pressure, thereby prolonging the lifespan of the linear generator. [ABSTRACT FROM AUTHOR]

A series of experimental studies established that the differing morphologies of the phase diagrams versus hole doping nh of the various cuprate families are mostly controlled by defects and disorder. In the minimally disordered cuprate Yttrium Baryum Copper Oxide (YBCO) we introduced controlled detfects that allowed us to probe the metallic and superconducting states. We demonstrate that the extent of the spin glass phase and the superconducting dome can be controlled by the concentration of spinless (Zn, Li) impurities substituted on the planar Cu sites. NMR frequency shift measurements establish that these defects induce, in their vicinity, a cloud with a Kondo-like paramagnetic behavior. Its "Kondo" temperature and spatial extent differ markedly between the pseudogap and strange metal regimes. We have performed transport measurements on single crystals with a controlled content of in-plane vacancies introduced by electron irradiation. At high T, the inelastic scattering of the carriers has been found independent of disorder and completely governed by the excitations of the correlated electronic state. The low T upturns in the resistivity associated with single-site Kondo-like scattering are qualitatively in agreement with local magnetism induced by spinless impurities. The apparent metal insulator crossover is only detected for a very large defect content, and part of the large resistivity upturn remains connected with Kondo-like paramagnetism. In the superconducting state, the defect-induced reduction of Tc scales linearly with the increase in residual resistivity induced by disorder. High-field magnetoresistance experiments permit us to determine the paraconductivity due to superconducting fluctuations. The latter vanishes beyond a temperature T'c and a field H'c that both decrease with increasing in-plane defect content. In the pseudogap regime, the weaker decrease of T'c with respect to that of Tc reveals a large loss of superconducting phase coherence in the presence of disorder. In light of our experimental results, we initiate a discussion of its interplay with pair breaking. Our data also permit us to confirm that the differing phase diagrams are due to competing orders or disorders that are family-specific. In the ideal phase diagram of a disorder-free cuprate, 2D superconductivity should persist at low doping. This ensemble of experimental results provides serious challenges for the theoretical understanding of superconductivity in these correlated electron systems. [ABSTRACT FROM AUTHOR]

We investigated the effect of 0.6 MeV proton irradiation on the superconducting and normal-state properties of thin-film YBa 2 Cu 3 O 7 − δ superconductors. A thin-film YBCO superconductor (≈567 nm thick) was subject to a series of proton irradiations with a total fluence of 7.6 × 10 16   p / cm 2 . Upon irradiation, T c was drastically decreased from 89.3 K towards zero with a corresponding increase in the normal-state resistivity above T c . This increase in resistivity, which indicates an increase in defects inside the thin-film sample, can be converted to the dimensionless scattering rate. We found that the relation between T c and the dimensionless scattering rate obtained during proton irradiation approximates the generalized d-wave Abrikosov–Gor'kov theory better than the previous results obtained from electron irradiations. This is an unexpected result, since the electron irradiation is known to be most effective to suppress superconductivity over other heavier ion irradiations such as proton irradiation. In comparison with the previous irradiation studies, we found that the result can be explained by two facts. First, the dominant defects created by 0.6 MeV protons can be point-like when the implantation depth is much longer than the sample thickness. Second, the presence of defects on all element sites is important to effectively suppress T c . [ABSTRACT FROM AUTHOR]

While closing their famous paper entitled "Pseudogap: friend or foe of high-Tc?" Norman, Pines, and Kallin underlined that before we have a microscopic theory, we must have a consistent phenomenology. This was in 2005. As it turns out in 2006, a phenomenological theory of the pseudogap state was proposed by Gor'kov and Teitel'baum. This originated from their careful analysis of the Hall effect data, and it has been very successful model as numerous investigations over the years have shown. In this mini-review, the essence of the idea of Gor'kov and Teitel'baum is presented. The pseudogap obtained by them from the Hall effect data agrees very well with that obtained from the ARPES data. This famous Gor'kov–Teitel'baum thermal activation model (in short GTTA model) not only presents a consistent phenomenology of the pseudogap state, but also rationalizes the Hall angle data, and it presents a strong case against the famous "two-relaxation times" idea of Anderson and collaborators. [ABSTRACT FROM AUTHOR]

Superconducting magnets based on high-temperature superconductors (HTSs) have become critical components in cutting-edge technologies such as advanced medical applications. In HTSs, weak links of superconductivity are inevitable at high-angle grain boundaries (GBs). Thus, two adjacent grains should be crystallographically aligned within the critical angle (θc), for which the intergrain critical current density (Jc) starts to decrease exponentially. The θc of several iron-based superconductors (IBSs) is larger than that of cuprates. However, the decreases in both θc and intergrain Jc under magnetic fields for IBSs are still substantial, hampering their applications in polycrystalline forms. Here, we report that potassium-doped BaFe2As2 (Ba122:K) exhibits superior GB performance to that of previously reported IBSs. A transport Jc of over 0.1 MA/cm2 across [001]-tilt GBs with misorientation angles up to θGB = 24° was recorded even at 28 K, which is a required level for practical applications. Additionally, even in an applied magnetic field, θc was unaltered, and the decay of the intergrain Jc was small. Our results highlight the exceptional potential of Ba122:K for polycrystalline applications and pave the way for next-generation superconducting magnets. We have fabricated artificial grain boundaries in K-doped BaFe2As2 (Ba122:K), one of the Fe-based superconductors. The crystalline orientation map, acquired through the scanning precession electron diffraction measurements, revealed that spontaneous connectivity modification occurred at the grain boundary, which may mitigate weak-link behavior. Specifically, a self-field critical current density Jc of over 0.1 MA/cm2 across the grain boundary with misorientation angles up to 24° was recorded even at 28 K. This performance surpasses the grain boundary properties of hitherto reported Fe-based superconductors. Our results highlight the exceptional potential of Ba122:K for polycrystalline applications and pave the way for next-generation superconducting magnets. [ABSTRACT FROM AUTHOR]

In the underdoped n-type cuprate Nd2-xCexCuO4, long-range antiferromagnetic order reconstructs the Fermi surface, resulting in a putative antiferromagnetic metal with small Fermi pockets. Using angle-resolved photoemission spectroscopy, we observe an anomalous energy gap, an order of magnitude smaller than the antiferromagnetic gap, in a wide portion of the underdoped regime and smoothly connecting to the superconducting gap at optimal doping. After considering all the known ordering tendencies in tandem with the phase diagram, we hypothesize that the normal-state gap in the underdoped n-type cuprates originates from Cooper pairing. The high temperature scale of the normal-state gap raises the prospect of engineering higher transition temperatures in the n-type cuprates comparable to those of the p-type cuprates. [ABSTRACT FROM AUTHOR]

Strongly correlated electron materials are often characterized by competition and interplay of multiple quantum states. For example, in high-temperature cuprate superconductors unconventional superconductivity, spin- and charge-density wave orders coexist. A key question is whether competing states coexist on the atomic scale or if they segregate into distinct regions. Using X-ray diffraction, we investigate the competition between charge order and superconductivity in the archetypal cuprate La2−xBaxCuO4, around x = 1/8-doping, where uniaxial stress restores optimal 3D superconductivity at σ3D ≈ 0.06 GPa. We find that the charge order peaks and the correlation length along the stripe are strongly reduced up to σ3D. Upon the increase of stress beyond this point, no further changes were observed. Simultaneously, the charge order onset temperature only shows a modest decrease. Our findings suggest that optimal 3D superconductivity is not linked to the absence of charge stripes but instead requires their arrangement into smaller regions. Our results provide insight into the length scales over which the interplay between superconductivity and charge order takes place. In many quantum materials, different electronic phases can coexist or compete with one another. In this work uniaxial pressure is used to achieve the spatial distribution of charge order that maximizes the superconducting transition temperature. [ABSTRACT FROM AUTHOR]

Superconducting infinite-layer (IL) nickelates offer a new platform for investigating the long-standing problem of high-temperature superconductivity. Many models were proposed to understand the superconducting mechanism of nickelates based on the calculated electronic structure, and the multiple Fermi surfaces and multiple orbitals involved create complications and controversial conclusions. Over the past five years, the lack of direct measurements of the electronic structure has hindered the understanding of nickelate superconductors. Here we fill this gap by directly resolving the electronic structures of the parent compound LaNiO2 and superconducting La0.8Ca0.2NiO2 using angle-resolved photoemission spectroscopy. We find that their Fermi surfaces consist of a quasi-2D hole pocket and a 3D electron pocket at the Brillouin zone corner, whose volumes change upon Ca doping. The Fermi surface topology and band dispersion of the hole pocket closely resemble those observed in hole-doped cuprates. However, the cuprate-like band exhibits significantly higher hole doping in superconducting La0.8Ca0.2NiO2 compared to superconducting cuprates, highlighting the disparities in the electronic states of the superconducting phase. Our observations highlight the novel aspects of the IL nickelates, and pave the way toward the microscopic understanding of the IL nickelate family and its superconductivity. [ABSTRACT FROM AUTHOR]

Information on the state of research on the effect of hydrogen on the superconducting properties of various compounds is presented. The review consists of an introduction, one appendix and four sections: methods for the synthesis of modern hydrogen-containing superconductors, experimental studies of the properties of hydrogen-containing superconductors, mechanisms of the influence of hydrogen on superconductivity, problems and prospects of hydrogen-containing superconductors. [ABSTRACT FROM AUTHOR]

Extensive research on transition metal perovskite oxides as electrodes in solid oxide cells (SOC) has highlighted the potential ability of Fe-based perovskite oxides to catalyze oxygen reduction/evolution reactions (ORR/OER). The layered perovskite-type system YSr2Cu2FeO7+δ has been reported to possess attractive electrocatalytic properties. This work applies density functional theory (DFT) calculations to investigate oxygen ion diffusion in the YSr2Cu2FeO7+δ system. For δ = 0.5, it is found that in the most stable configuration, the oxygen vacancies in the FeO1+δ plane are arranged to form Fe ions in tetrahedral, square pyramid, and octahedral coordination. Ab initio molecular dynamics (AIMD) simulations for YSr2Cu2FeO7.5 (δ = 0.5) yield an oxygen ion diffusion coefficient of 1.28 × 10−7 cm2/s at 500 °C (Ea = 0.37 eV). Complementary results for YSr2Cu2FeO7.2 (δ = 0.2) and YSr2Cu2FeO7.75 (δ = 0.75) indicate that the oxygen diffusion occurs in the FeO1+δ plane, and depends on the oxygen vacancies distribution around the Fe centers. [ABSTRACT FROM AUTHOR]

Charge order has been a central focus in the study of cuprate high-temperature superconductors due to its intriguing yet not fully understood connection to superconductivity. Recent advances in resonant inelastic x-ray scattering (RIXS) in the soft x-ray regime have enabled the first momentum-resolved studies of dynamic charge order correlations in the cuprates. This progress has opened a window for a more nuanced investigation into the mechanisms behind the formation of charge order (CO) correlations. This review provides an overview of RIXS-based measurements of dynamic CO correlations in various cuprate materials. It specifically focuses on electron-doped cuprates and Bi-based hole-doped cuprates, where the CO-related RIXS signals may reveal signatures of the effective Coulomb interactions. This aims to explore a connection between two central phenomena in the cuprates: strong Coulomb correlations and CO-forming tendencies. Finally, we discuss current open questions and potential directions for future RIXS studies as the technique continues to improve and mature, along with other probes of dynamic correlations that would provide a more comprehensive picture.

We demonstrate a method for fabricating a high-quality AlOx-based planar tunnel junction using atomic layer deposition, integrated with the exfoliation and transfer techniques for van der Waals (vdW) materials. The tunneling spectroscopy results on exfoliated Bi2Sr2CaCu2O8+δ and 2H-NbSe2 vdW superconductors are highly consistent with that obtained by ultrahigh vacuum scanning tunneling spectroscopy on atomically clean surfaces. The planar tunneling devices enable high-precision spectroscopy over a wide range of temperatures and magnetic fields and reveal novel features and stark contrast between high-TC cuprates and conventional superconductors. This method represents a universally applicable technique for probing the electronic structure of various two-dimensional vdW materials. [ABSTRACT FROM AUTHOR]

Recently, high-temperature superconductivity has been found at the interface between two Mott insulators, PrBa2Cu3O7 and La2CuO4. In this work, we demonstrate our tuning of this interface superconductor by ionic liquid gating. By varying gate voltage, VG, a superconductor–insulator phase transition was achieved. Hall-effect measurements suggest that the carrier density, which can be tuned continuously from 1.86 × 1014 to 3.78 × 1014 cm−2 for VG varying from −0.3 to −3 V, is the tuning parameter. A finite-size scaling analysis was used to analyze the superconductor–insulator phase transition, which gives a critical resistance of 14–17 kΩ and a critical exponent of zν ≈ 1.3–1.4. These values are comparable with those obtained in previous studies on ultrathin clean cuprate films gated by ionic liquid. [ABSTRACT FROM AUTHOR]

Spin- and charge- stripe order has been extensively studied in the superconducting cuprates, among which underdoped La2−xSrxCuO4 (LSCO) is an archetype with static spin stripes at low temperatures. An intriguing, but not completely understood, phenomenon in LSCO is that the stripes are tilted away from the high-symmetry Cu-Cu directions. Using high-resolution neutron scattering on LSCO with x = 0.12, we find two coexisting phases at low temperatures, one with static spin stripes and the other with fluctuating ones, both sharing the same tilt angle. Our numerical calculations using the doped Hubbard model elucidate the tilting's origin, attributing it to anisotropic next-nearest neighbor hopping t ′ , consistent with the material's slight orthorhombicity. Our results underscore the model's success in describing specific details of the ground state of this real material and highlight the role of t ′ in the Hamiltonian, revealing the delicate interplay between stripes and superconductivity across theoretical and experimental contexts. Cuprate superconductors have interesting charge and spin ordering patterns in the form of stripes. By combining experimental and numerical tools, the authors reveal that the stripes are always tilted from the underlying lattice directions, with the origin well explained by the anisotropy of the next-nearest neighbor electron hopping. [ABSTRACT FROM AUTHOR]

The low-temperature electrical transport in the normal-state of overdoped cuprate superconductors is investigated based on the t-J model. The momentum relaxation due to the umklapp scattering between electrons by the exchange of the effective spin propagator is employed to evaluate the electrical resistivity within the framework of the Boltzmann transport theory. It is shown that the quadratic temperature dependence of the resistivity develops in the far-lower-temperature region, and is followed by a nonlinear temperature dependence of the resistivity in an extremely-narrow-crossover region and a linear temperature dependence of the resistivity in the low-temperature region. The obtained results also show that the same spin excitation governs both superconductivity and the electron umklapp scattering responsible for the low-temperature linear in temperature resistivity in the overdoped regime. [ABSTRACT FROM AUTHOR]

The interfaces between superconductors and other materials have long been established as being an important part in the exploration of new physics to aid in our understanding of superconductivity and open us up to new technological advancements. Herein this article we analyse the recent progress made in the understanding of superconductivity at the interfaces involving a wide range of functional materials, mostly looking at two-dimensional (2D) systems. We start off in the first half of this review by focusing on magnetic and superconductive hybrid heterostructures, as well as the resulting physical phenomena from these systems. The first is a section on vortex and anti-vortex phenomena; the second key area is ferromagnet–superconductor hybrid phenomena with particular interest of magnetic skyrmions, the third is the novel frontier based on 2D magnetic and superconductive interfaces particularly examining Ising superconductivity at these interfaces; the fourth is superconductivity at anti-ferromagnetic interfaces and finally half-metals at superconducting interfaces. The second half of this review focuses on superconductivity at insulating and other functional interfaces. Examining firstly, Mott insulator interfaces with wide ranging discussions about how such interfaces can enhance our understanding in high-temperature superconductive cuprates and other unconventional superconductor systems such as the nickelates; in the second section the interface of 2D and 3D ferroelectric materials with superconductors with a key emphasis on devices that have been developed to control the superconducting phase; Topological insulators at interfaces with superconductors is the third section; and lastly 2D twisted material interfaces are explored, including the newly discovered magic angle interfaces discovered with graphene and other van Der Waals materials. It is anticipated that this review will lead to further interest in such interfaces to improve our understanding and expose the exotic science behind these interfaces. [Display omitted] [ABSTRACT FROM AUTHOR]

Unconventional superconductivity on a honeycomb lattice has received increasing interest since the discovery of graphene primarily due to the similarities between materials with a honeycomb lattice and cuprate superconductors. Many theoretical studies have been conducted on superconductivity on a honeycomb lattice, however, a consistent picture is still lacking. In this paper, we have extended the theory of kinetic-energy-driven superconductivity, which has been developed to investigate unconventional superconductivity in cuprate superconductors, to explore superconductivity on a honeycomb lattice within the t-J model. Our results demonstrate that the charge-carrier pair gap parameter with d x 2 − y 2 + i d x y -wave symmetry exhibits a dome-like shape as a function of doping, with superconductivity emerging at a certain doping concentration and disappearing at high doping levels, similar to what has been observed in cuprate and cobaltate superconductors. Furthermore, the charge-carrier pair gap parameter decreases with increasing the value of J ∕ t (the ratio between the antiferromagnetic exchange coupling constant and the nearest-neighbor hopping integral), and approaches zero when J ∕ t reaches a sufficiently large value. This indicates that the antiferromagnetic order will suppress the superconducting state and a sufficiently strong exchange coupling will completely destroy the superconductivity. Taking into account our present results together with the corresponding results of cuprate and cobaltate superconductors, it appears that the dome-like shape of the doping dependence of the charge-carrier pair gap parameter may be a common feature in doped Mott insulators. [ABSTRACT FROM AUTHOR]

Sr2IrO4 has attracted considerable attention due to its structural and electronic similarities to La2CuO4, the parent compound of high-Tc superconducting cuprates. It was proposed as a strong spin-orbit-coupled Jeff = 1/2 Mott insulator, but the Mott nature of its insulating ground state has not been conclusively established. Here, we use ultrafast laser pulses to realize an insulator-metal transition in Sr2IrO4 and probe the resulting dynamics using time-and angle-resolved photoemission spectroscopy. We observe a gap closure and the formation of weakly renormalized electronic bands in the gap region. Comparing these observations to the expected temperature and doping evolution of Mott gaps and Hubbard bands provides clear evidence that the insulating state does not originate from Mott correlations. We instead propose a correlated band insulator picture, where antiferromagnetic correlations play a key role in the gap opening. More broadly, our results demonstrate that energy-momentum-resolved nonequilibrium dynamics can be used to clarify the nature of equilibrium states in correlated materials. [ABSTRACT FROM AUTHOR]

We present a way to fabricate bicrystal Josephson junctions of high-Tc cuprate superconductors that are not grown on bulk bicrystalline substrates. Based on vector substrate technology, this approach makes use of a few tens-of-nanometer-thick bicrystalline membranes transferred onto conventional substrates. We demonstrate 24° [001]-tilt YBa2Cu3O7−x Josephson junctions fabricated on sapphire single crystals by utilizing 10-nm-thick bicrystalline SrTiO3 membranes. This technique allows one to manufacture bicrystalline Josephson junctions of high-Tc superconductors on a large variety of bulk substrate materials, providing distinctive degrees of freedom in designing the junctions and their electronic properties. Furthermore, it offers the capability to replace the fabrication of bulk bicrystalline substrates with thin-film growth methods. [ABSTRACT FROM AUTHOR]

Unconventional superconductivity often couples to other electronic orders in a cooperative or competing fashion. Identifying external stimuli that tune between these two limits is of fundamental interest. Here, we show that strain perpendicular to the copper-oxide planes couples directly to the competing interaction between charge stripe order and superconductivity in La1.88Sr0.12CuO4 (LSCO). Compressive c-axis pressure amplifies stripe order within the superconducting state, while having no impact on the normal state. By contrast, strain dramatically diminishes the magnetic field enhancement of stripe order in the superconducting state. These results suggest that c-axis strain acts as tuning parameter of the competing interaction between charge stripe order and superconductivity. This interpretation implies a uniaxial pressure-induced ground state in which the competition between charge order and superconductivity is reduced. Tuning superconductivity and its interplay with other phases in cuprates yields insights into the underlying physics of this material class. Here, the authors performed a hard x-ray diffraction experiment on La1.88Sr0.12CuO4 showing that uniaxial pressure along the c-axis acts as a direct tuning parameter of the competition between superconductivity and charge order. [ABSTRACT FROM AUTHOR]