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Abstract The aim of the current study is to investigate the impact of layer coupling on the characteristics of high TC superconductor Nd2‐xCexCuO4 (NCCO). In this study, the intra‐ and inter‐layer couplings are taken into consideration. By applying the double time Green's function (GF) technique and formulating a model Hamiltonian, the transition temperature (TC) of superconductor Nd2‐xCexCuO4 is computed quantitatively by considering the intra‐ and inter‐layer interactions as independent variables. By increasing the layer interactions, the increase in TC is observed. Furthermore, TC is calculated by taking into consideration different number of interlayer interactions as independent variables which subsequently resulted in the enhancement of TC. Besides, TC has been computed as a function of electron doping as a result of which a dome shaped figure has been perceived in the temperature versus doping phase diagram. The superconducting order parameter (Δ) has been also reckoned as a function of temperature and is observed to gradually decrease as temperature increases and eventually vanishes at TC. A slight increment in TC is observed as the doping values of charge carriers increase. Our findings are discussed in connection with the experimental studies of superconductivity (SC) in Nd2CuO4 based layered compounds.

The aim of the current study is to investigate the impact of layer coupling on the characteristics of high TC superconductor Nd2‐xCexCuO4 (NCCO). In this study, the intra‐ and inter‐layer couplings are taken into consideration. By applying the double time Green's function (GF) technique and formulating a model Hamiltonian, the transition temperature (TC) of superconductor Nd2‐xCexCuO4 is computed quantitatively by considering the intra‐ and inter‐layer interactions as independent variables. By increasing the layer interactions, the increase in TC is observed. Furthermore, TC is calculated by taking into consideration different number of interlayer interactions as independent variables which subsequently resulted in the enhancement of TC. Besides, TC has been computed as a function of electron doping as a result of which a dome shaped figure has been perceived in the temperature versus doping phase diagram. The superconducting order parameter (Δ) has been also reckoned as a function of temperature and is observed to gradually decrease as temperature increases and eventually vanishes at TC. A slight increment in TC is observed as the doping values of charge carriers increase. Our findings are discussed in connection with the experimental studies of superconductivity (SC) in Nd2CuO4 based layered compounds. [ABSTRACT FROM AUTHOR]

In conventional superconductors, electron-phonon coupling plays a dominant role in generating superconductivity. In high-temperature cuprate superconductors, the existence of electron coupling with phonons and other boson modes and its role in producing high-temperature superconductivity remain unclear. The evidence of electron-boson coupling mainly comes from angle-resolved photoemission (ARPES) observations of ∼70-meV nodal dispersion kink and ∼40-meV antinodal kink. However, the reported results are sporadic and the nature of the involved bosons is still under debate. Here we report findings of ubiquitous two coexisting electronmode couplings in cuprate superconductors. By taking ultrahigh-resolution laser-based ARPES measurements, we found that the electrons are coupled simultaneously with two sharp modes at ∼70meV and ∼40meV in different superconductors with different dopings, over the entire momentum space and at different temperatures above and below the superconducting transition temperature. These observations favor phonons as the origin of the modes coupled with electrons and the observed electron-mode couplings are unusual because the associated energy scales do not exhibit an obvious energy shift across the superconducting transition. We further find that the wellknown “peak-dip-hump” structure, which has long been considered a hallmark of superconductivity, is also omnipresent and consists of “peak-double dip-double hump” finer structures that originate from electron coupling with two sharp modes. These results provide a unified picture for the ∼70-meV and ∼40-meV energy scales and their evolutions with momentum, doping and temperature. They provide key information to understand the origin of these energy scales and their role in generating anomalous normal state and high-temperature superconductivity. [ABSTRACT FROM AUTHOR]

We report results of large-scale ground-state density matrix renormalization group (DMRG) calculations on t-[Formula: see text]-J cylinders with circumferences 6 and 8. We determine a rough phase diagram that appears to approximate the two-dimensional (2D) system. While for many properties, positive and negative [Formula: see text] values ([Formula: see text]) appear to correspond to electron- and hole-doped cuprate systems, respectively, the behavior of superconductivity itself shows an inconsistency between the model and the materials. The [Formula: see text] (hole-doped) region shows antiferromagnetism limited to very low doping, stripes more generally, and the familiar Fermi surface of the hole-doped cuprates. However, we find [Formula: see text] strongly suppresses superconductivity. The [Formula: see text] (electron-doped) region shows the expected circular Fermi pocket of holes around the [Formula: see text] point and a broad low-doped region of coexisting antiferromagnetism and d-wave pairing with a triplet p component at wavevector [Formula: see text] induced by the antiferromagnetism and d-wave pairing. The pairing for the electron low-doped system with [Formula: see text] is strong and unambiguous in the DMRG simulations. At larger doping another broad region with stripes in addition to weaker d-wave pairing and striped p-wave pairing appears. In a small doping region near [Formula: see text] for [Formula: see text], we find an unconventional type of stripe involving unpaired holes located predominantly on chains spaced three lattice spacings apart. The undoped two-leg ladder regions in between mimic the short-ranged spin correlations seen in two-leg Heisenberg ladders.

This study discusses the conditions for the occurrence of two-dimensional superconductivity under the action of an electric field on an La2 – xSrxCuO4 plate at a temperature lower than the maximum temperature of the superconducting transition, but when the concentration of charge carriers falls outside the superconductivity range. The study is carried out for a lanthanum-strontium cuprate plate at various hole concentrations, as well as temperature, and potential differences. A quasi-two-dimensional superconducting layer arises near the surface of the plate. The thickness of the superconducting layer is several angstroms and independent of the field strength in the range investigated. The thickness depends only on the concentration of holes and temperature. In addition, the distance of the superconducting layer from the edge of the plate is found to be a function of all three factors. The conditions used for conducting the experiment are also formulated. [ABSTRACT FROM AUTHOR]

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconducting transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+δ (Bi2201) and bilayer Bi2Sr2CaCu2O8+δ (Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tc and doping (p) or pressure (P) at higher pressures. The Tc of underdoped Bi2201 initially increases from 9.6 K at ambient to a peak at 23 K at 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above 40 GPa, Tc rises rapidly without any sign of saturation up to 30 K at 51 GPa. Similarly, the Tc for the slightly overdoped Bi2212 increases after passing a broad valley between 20 and 36 GPa and reaches 90 K without any sign of saturation at 56 GPa. We have, therefore, attributed this Tc resurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3[Formula: see text] and the O 2p bands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br2Sr2Ca2Cu3O10+δ (Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high-temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures.

The Y1–xLixBa2Cu3O7–δ polycrystalline bulk superconductors doped with Li substituting at the Y site at different concentrations (x = 0, 0.01, 0.02, 0.1) were prepared using the citrate-gel method to study the effects of doping on the superconducting temperature and critical current density. The question was whether Li addition characterized by a high Debye frequency would have any positive effects on Tc. The optimum citrate-gel and heat treatment conditions were identified as those yielding samples with a maximum grain size on the order of 50 μm (up to the optimum Li doping level, x = 0.01). Li substitution at the Y site was verified by structural, electrical, and magnetic measurements of the produced samples, whereas X-ray diffraction (XRD) analysis revealed the formation of a pure phase with no visible impurity phases. Moreover, AC magnetic susceptibility measurements showed no increase in the superconducting transition temperature Tc, consistent with the predicted results obtained by machine learning method, although it was theoretically expected to increase owing to the high Debye frequency of Li. This observation is consistent with magnetic coupling models for pairing mechanism in cuprates. Finally, because of the optimum conditions of the preparation procedure, nearly identical values of the critical current density (Jc) were recorded for samples with different Li doping levels (up to the optimum Li doping level). It was found that improved compound preparation conditions would have a critical and extensive effect on Jc enhancement, with nearly no Tc suppression. [ABSTRACT FROM AUTHOR]

Understanding electronic properties that violate the Landau Fermi liquid paradigm in cuprate superconductors remains a major challenge in condensed-matter physics. The strange metal state in overdoped cuprates that exhibits linear-in-temperature scattering rate and direct current (dc) resistivity is a particularly puzzling example. Here, we compute the electronic scattering rate in the two-dimensional Hubbard model using cluster generalization of dynamical mean-field theory. We present a global phase diagram documenting an apparent non-Fermi liquid phase, in between the pseudogap and Fermi liquid phase in the doped Mott insulator regime. We discover that in this non-Fermi liquid phase, the electronic scattering rate γk (T) can display linear temperature dependence as temperature T goes to zero. In the temperature range that we can access, the T-dependent scattering rate is isotropic on the Fermi surface, in agreement with recent experiments. Using fluctuation diagnostic techniques, we identify antiferromagnetic fluctuations as the physical origin of the T-linear electronic scattering rate. [ABSTRACT FROM AUTHOR]

In cuprate superconductors, due to strong electronic correlations, there are multiple intertwined orders which either coexist or compete with superconductivity. Among them, the antiferromagnetic (AF) order is the most prominent one. In the region where superconductivity sets in, the long-range AF order is destroyed. Yet the residual short-range AF spin fluctuations are present up to a much higher doping, and their role in the emergence of the superconducting phase is still highly debated. Here, by using a spin-polarized scanning tunneling microscope, we directly visualize an emergent incommensurate AF order in the nearby region of Fe impurities embedded in the optimally doped Bi2Sr2CaCu2O8+δ (Bi2212). Remarkably, the Fe impurities suppress the superconducting coherence peaks with the gapped feature intact, but pin down the ubiquitous short-range incommensurate AF order. Our work shows an intimate relation between antiferromagnetism and superconductivity. [ABSTRACT FROM AUTHOR]

In cuprate superconductors, due to strong electronic correlations, there are multiple intertwined orders which either coexist or compete with superconductivity. Among them, the antiferromagnetic (AF) order is the most prominent one. In the region where superconductivity sets in, the long-range AF order is destroyed. Yet the residual short-range AF spin fluctuations are present up to a much higher doping, and their role in the emergence of the superconducting phase is still highly debated. Here, by using a spin-polarized scanning tunneling microscope, we directly visualize an emergent incommensurate AF order in the nearby region of Fe impurities embedded in the optimally doped Bi2Sr2CaCu2O8+δ (Bi2212). Remarkably, the Fe impurities suppress the superconducting coherence peaks with the gapped feature intact, but pin down the ubiquitous short-range incommensurate AF order. Our work shows an intimate relation between antiferromagnetism and superconductivity. [ABSTRACT FROM AUTHOR]

We report results of large-scale ground-state density matrix renormalization group (DMRG) calculations on t-t′-J cylinders with circumferences 6 and 8. We determine a rough phase diagram that appears to approximate the two-dimensional (2D) system. While for many properties, positive and negative t′ values (t′/t=±0.2) appear to correspond to electron- and hole-doped cuprate systems, respectively, the behavior of superconductivity itself shows an inconsistency between the model and the materials. The t′<0 (hole-doped) region shows antiferromagnetism limited to very low doping, stripes more generally, and the familiar Fermi surface of the hole-doped cuprates. However, we find t′<0 strongly suppresses superconductivity. The t′>0 (electron-doped) region shows the expected circular Fermi pocket of holes around the (π,π) point and a broad low-doped region of coexisting antiferromagnetism and d-wave pairing with a triplet p component at wavevector (π,π) induced by the antiferromagnetism and d-wave pairing. The pairing for the electron low-doped system with t′>0 is strong and unambiguous in the DMRG simulations. At larger doping another broad region with stripes in addition to weaker d-wave pairing and striped p-wave pairing appears. In a small doping region near x=0.08 for t′∼−0.2, we find an unconventional type of stripe involving unpaired holes located predominantly on chains spaced three lattice spacings apart. The undoped two-leg ladder regions in between mimic the short-ranged spin correlations seen in two-leg Heisenberg ladders. [ABSTRACT FROM AUTHOR]

The thermal capacities of nanodimensional (nanocluster) cobalte (nickelite) - cuprate-manganites of lanthanum and sodium of LaNa2CoCuMnO6, LaNa2NiCuMnO6 were investigated with the calorimetry method on the IT-S-400 device in the temperature interval of 298,15 - 673 K. Based on the experimental data the equations of temperature dependence of thermal capacity of the studied compounds were set up. The temperature dependences of thermodynamic functions were estimated with using of measured values of thermal capacity and calculated value of standard entropy.

Atomically thin cuprates exhibiting a superconducting phase transition temperature similar to that of the bulk have recently been realized, although the device fabrication remains a challenge and limits the potential for many novel studies and applications. Here, we use an optical pump-probe approach to noninvasively study the unconventional superconductivity in atomically thin Bi 2 Sr 2 Ca 0.92 Y 0.08 Cu 2 O 8+δ (Y-Bi2212). Apart from finding an optical response due to the superconducting phase transition that is similar to that of bulk Y-Bi2212, we observe that the sign and amplitude of the pump-probe signal in atomically thin flakes vary significantly in different dielectric environments depending on the nature of the optical excitation. By exploiting the spatial resolution of the optical probe, we uncover the exceptional sensitivity of monolayer Y-Bi2212 to the environment. Our results provide the first optical evidence for the intralayer nature of the superconducting condensate in Bi2212 and highlight the role of double-sided encapsulation in preserving superconductivity in atomically thin cuprates.

Bulk Tl2Ba2Ca2Cu3Ox superconductor was synthesized and oxygenated. The critical temperature was determined to be 116.5 K from resistivity, 117.5 K from AC susceptibility (intra-grain) and 115.0 K from AC susceptibility (inter-grain). The critical current at 77.3 K, utilizing a non-contact Bean's method, is 189 A/cm2. After oxygenation, the sample contained 60% mass of the desired compound (X-ray diffraction measurement). The critical exponent in the closest vicinity of the critical temperature occurred to be 0.112 (AC susceptibility) and 0.259 (resistance). Further, from the critical temperature the susceptibility exponent was determined to be 0.779 and the resistance critical exponent was equal to 1.13. [ABSTRACT FROM AUTHOR]

The superconductivity of La2CuO4-based materials is known to be achievable by doping holes in Cu ions. In this study, the hole content was tuned by mixing anion sites with oxygen and sulfur. The substitution of La1.7Sr0.3CuO4 with sulfur led to the recovery of superconductivity from overdoped regions, a result indicative of decreased hole content. Precise structural analysis revealed that the majority of sulfur is incorporated into impurities in the SrSO4 phase, which decreases the hole content of Cu ions via a decrease in the Sr content; however, the superconductivity cannot be interpreted by this mechanism alone. Supporting evidence for the incorporation of sulfur into the La1.7Sr0.3CuO4Sx phase was obtained by an investigation of the composition dependence of the lattice parameters and X-ray photoelectron spectroscopy. Substitution of oxygen with sulfur, which served to decrease the hole content, as a means of recovering superconductivity was shown to act.

Thallium based Tl2Ba2Ca2Cu3Ox superconductors were synthesized in double silver foil at 880 °C for 30 min under flowing oxygen gas. Additional oxygenations, each lasting 20 h, were performed at temperatures varying from 700 °C to 820 °C to increase the critical temperature and the critical current of the superconductor. Optimal temperature of the oxygenation was of 760 °C. [ABSTRACT FROM AUTHOR]

Thallium based Tl2Ba2Ca2Cu3Ox superconductors were synthesized in double silver foil at 880 °C for 30 min under flowing oxygen gas. Additional oxygenations, each lasting 20 h, were performed at temperatures varying from 700 °C to 820 °C to increase the critical temperature and the critical current of the superconductor. Optimal temperature of the oxygenation was of 760 °C. [ABSTRACT FROM AUTHOR]

An investigation has been carried out on the effects of praseodymium doping in Sm3−xPrxBa5Cu8O19 for different values of x. Results indicate that the transition temperature reduces almost linearly with x. Based on the Abrikosov–Gor'kov pair-breaking theory, it has been concluded that the exchange interaction constant is large (Jex = 110 meV) in the Sm3Ba5Cu8O19 compound. In addition, it seems that the hybridization of Pr4f states with O2p–Cu3d states has an important role in the depression of transition temperature of Sm3−xPrxBa5Cu8O19 for the Pr content < 10%. However, for the higher values of Pr, the two observed plateaus at the transition temperatures of ~ 60 K and ~ 17 K, respectively, resemble the structural phase transitions due to oxygen reduction in the YBa2Cu3O7 compound and the antiferromagnetic phase formation in the PrBa2Cu3O7 compound. It seems that depending on the Pr content, the pair-breaking, structural effects and hole localization are responsible for the reduction in the transition temperature. [ABSTRACT FROM AUTHOR]

The thermal capacities of nanodimensional (nanocluster) cobalte (nickelite) - cuprate-manganites of lanthanum and sodium of LaNa2CoCuMnO6, LaNa2NiCuMnO6 were investigated with the calorimetry method on the IT-S-400 device in the temperature interval of 298,15 - 673 K. Based on the experimental data the equations of temperature dependence of thermal capacity of the studied compounds were set up. The temperature dependences of thermodynamic functions were estimated with using of measured values of thermal capacity and calculated value of standard entropy. [ABSTRACT FROM AUTHOR]

The cuprate superconductors display several characteristic temperatures which decrease as the material composition is doped, tracing lines across the temperature-doping phase diagram. Foremost among these is the pseudogap transition. At a higher temperature, a peak is seen in the magnetic susceptibility, and changes in symmetry and in transport are seen at other characteristic temperatures. We report a meta-analysis of all measurements of characteristic temperatures well above Tc in strontium-doped lanthanum cuprate (LSCO) and oxygen-doped yttrium barium copper oxide (YBCO). The experimental corpus shows that the pseudogap line is one of a family of four straight lines which stretches across the phase diagram from low to high doping, and from Tc up to 700 K. These lines all originate from a single point near the overdoped limit of the superconducting phase and increase as doping is reduced. The slope of the pseudogap lines is quantized, with the second, third, and fourth lines having slopes that are respectively 1/2, 1/3, and 1/4 of the slope of the highest line. This pattern suggests that the cuprates host a single mother phase controlled by a 2-D sheet density which is largest at zero doping and which decreases linearly with hole density, and that the pseudogap lines, charge density wave order, and superconductivity are all subsidiary effects supported by the mother phase. [ABSTRACT FROM AUTHOR]

The high-temperature conductivity of the perovskite oxides of a La4BaCu5O13+δ (LBCO) thin film prepared by RF sputtering deposition and thermal annealing has been studied. While the bulk LBCO compound was metallic, the LBCO film deposited on a Si substrate by sputtering and a post annealing process showed semiconductor-like conduction, which is considered to be due to the defects and poor grain connectivity in the LBCO film on the Si substrate. The LBCO film deposited on a SrTiO3 substrate was of high film quality and showed metallic conduction. When the cation site Cu was substituted by Co, the electrical conductivity of the LBCO film increased further and its temperature dependence became smaller. The transport properties of LBCO films are investigated to understand its carrier generation mechanism.

In conventional superconductors, electron-phonon coupling plays a dominant role in generating superconductivity. In high-temperature cuprate superconductors, the existence of electron coupling with phonons and other boson modes and its role in producing high-temperature superconductivity remain unclear. The evidence of electron-boson coupling mainly comes from angle-resolved photoemission (ARPES) observations of [Formula: see text]70-meV nodal dispersion kink and [Formula: see text]40-meV antinodal kink. However, the reported results are sporadic and the nature of the involved bosons is still under debate. Here we report findings of ubiquitous two coexisting electron-mode couplings in cuprate superconductors. By taking ultrahigh-resolution laser-based ARPES measurements, we found that the electrons are coupled simultaneously with two sharp modes at [Formula: see text]70meV and [Formula: see text]40meV in different superconductors with different dopings, over the entire momentum space and at different temperatures above and below the superconducting transition temperature. These observations favor phonons as the origin of the modes coupled with electrons and the observed electron-mode couplings are unusual because the associated energy scales do not exhibit an obvious energy shift across the superconducting transition. We further find that the well-known "peak-dip-hump" structure, which has long been considered a hallmark of superconductivity, is also omnipresent and consists of "peak-double dip-double hump" finer structures that originate from electron coupling with two sharp modes. These results provide a unified picture for the [Formula: see text]70-meV and [Formula: see text]40-meV energy scales and their evolutions with momentum, doping and temperature. They provide key information to understand the origin of these energy scales and their role in generating anomalous normal state and high-temperature superconductivity.

The CuO2 antiferromagnetic insulator is transformed by holedoping into an exotic quantum fluid usually referred to as the pseudogap (PG) phase. Its defining characteristic is a strong suppression of the electronic density-of-states D(E) for energies |E| < Δ*, where Δ* is the PG energy. Unanticipated broken-symmetry phases have been detected by a wide variety of techniques in the PG regime, most significantly a finite-Q density-wave (DW) state and a Q = 0 nematic (NE) state. Sublattice-phase-resolved imaging of electronic structure allows the doping and energy dependence of these distinct broken-symmetry states to be visualized simultaneously. Using this approach, we show that even though their reported ordering temperatures TDW and TNE are unrelated to each other, both the DW and NE states always exhibit their maximum spectral intensity at the same energy, and using independent measurements that this is the PG energy Δ*. Moreover, no new energy-gap opening coincides with the appearance of the DW state (which should theoretically open an energy gap on the Fermi surface), while the observed PG opening coincides with the appearance of the NE state (which should theoretically be incapable of opening a Fermi-surface gap). We demonstrate how this perplexing phenomenology of thermal transitions and energy-gap opening at the breaking of two highly distinct symmetries may be understood as the natural consequence of a vestigial nematic state within the pseudogap phase of Bi2Sr2CaCu2O8. [ABSTRACT FROM AUTHOR]

The observation of nonzero voltage transverse to the current flow, in zero magnetic field, is a sensitive indication of the nematic order in cuprate superconductors. But this effect should be carefully identified and differentiated from various conceivable experimental artifacts. Here we discuss in detail the five types of artifacts commonly encountered in transport experiments and explain how we rule out these possibilities by decisive experimental evidence. [ABSTRACT FROM AUTHOR]