The last decade witnessed significant progress in angle-resolved photoemission spectroscopy (ARPES) and its applications. Today, ARPES experiments with 2-meV energy resolution and $0.2\ifmmode^\circ\else\textdegree\fi{}$ angular resolution are a reality even for photoemission on solids. These technological advances and the improved sample quality have enabled ARPES to emerge as a leading tool in the investigation of the high-${T}_{c}$ superconductors. This paper reviews the most recent ARPES results on the cuprate superconductors and their insulating parent and sister compounds, with the purpose of providing an updated summary of the extensive literature. The low-energy excitations are discussed with emphasis on some of the most relevant issues, such as the Fermi surface and remnant Fermi surface, the superconducting gap, the pseudogap and $d$-wave-like dispersion, evidence of electronic inhomogeneity and nanoscale phase separation, the emergence of coherent quasiparticles through the superconducting transition, and many-body effects in the one-particle spectral function due to the interaction of the charge with magnetic and/or lattice degrees of freedom. Given the dynamic nature of the field, we chose to focus mainly on reviewing the experimental data, as on the experimental side a general consensus has been reached, whereas interpretations and related theoretical models can vary significantly. The first part of the paper introduces photoemission spectroscopy in the context of strongly interacting systems, along with an update on the state-of-the-art instrumentation. The second part provides an overview of the scientific issues relevant to the investigation of the low-energy electronic structure by ARPES. The rest of the paper is devoted to the experimental results from the cuprates, and the discussion is organized along conceptual lines: normal-state electronic structure, interlayer interaction, superconducting gap, coherent superconducting peak, pseudogap, electron self-energy, and collective modes. Within each topic, ARPES data from the various copper oxides are presented.

https://arxiv.org/pdf/cond-mat/0208504.pdf

Angle-resolved photoemission studies of the cuprate superconductors

Since the discovery of superconductivity above 30 K by Bednorz and M\"uller in the La copper oxide system, the critical temperature has been raised to 90 K in Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and to 110 and 125 K in Bi-based and Tl-based copper oxides, respectively. In the two years since this Nobel-prize-winning discovery, a large number of electronic structure calculations have been carried out as a first step in understanding the electronic properties of these materials. In this paper these calculations (mostly of the density-functional type) are gathered and reviewed, and their results are compared with the relevant experimental data. The picture that emerges is one in which the important electronic states are dominated by the copper $d$ and oxygen $p$ orbitals, with strong hybridization between them. Photon, electron, and positron spectroscopies provide important information about the electronic states, and comparison with electronic structure calculations indicates that, while many features can be interpreted in terms of existing calculations, self-energy corrections ("correlations") are important for a more detailed understanding. The antiferromagnetism that occurs in some regions of the phase diagram poses a particularly challenging problem for any detailed theory. The study of structural stability, lattice dynamics, and electron-phonon coupling in the copper oxides is also discussed. Finally, a brief review is given of the attempts so far to identify interaction constants appropriate for a model Hamiltonian treatment of many-body interactions in these materials.

Electronic structure of the high-temperature oxide superconductors

The broad spectrum of electronic and optical properties exhibited by oxides offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired Here we describe the use of reactive molecular-beam epitaxy and pulsed-laser deposition to synthesize functional oxides, including ferroelectrics, ferromagnets, and materials that are both at the same time Owing to the dependence of properties on direction, it is often optimal to grow functional oxides in particular directions to maximize their properties for a specific application But these thin film techniques offer more than orientation control; customization of the film structure down to the atomic-layer level is possible Numerous examples of the controlled epitaxial growth of oxides with perovskite and perovskite-related structures, including superlattices and metastable phases, are shown In addition to integrating functional oxides with conventional semiconductors, standard semiconductor practices involving epitaxial strain, confined thickness, and modulation doping can also be applied to oxide thin films Results of fundamental scientific importance as well as results revealing the tremendous potential of utilizing functional oxide thin films to create devices with enhanced performance are described

/pdf/a-thin-film-approach-to-engineering-functionality-into-51t9902h5j.pdf

A Thin Film Approach to Engineering Functionality into Oxides

Bulk superconductivity is reported in T12Ca2 Ba2 Cu3 Ox with a transition to zero resistance at ≃ 125 K, the highest transition temperature (Tc) yet found. Transmission electron spectroscopy shows that the unit cell is body-centered tetragonal and contains trilayer Cu perovskitelike units separated by bilayer TI-O units. (T c in this material varies from 118 to 125 K depending on preparation conditions. A high density of perovskitelike bilayer intergrowths are observed in the 118-K material, which we speculate result in the decreased (T c. A second structure containing only bilayer perovskitelike units—TI2 Ca1 Ba2Cu2Ox—is a bulk superconductor with Tv ranging from 95 to 108 K.

Bulk superconductivity at 125 K in Tl2Ca2Ba2Cu3Ox.

We examine the effect on the superconducting transition temperature ${(T}_{\mathrm{c}})$ of chemical inhomogeneities in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ and ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals. Cation disorder at the Sr crystallographic site is inherent in these materials and strongly affects the value of ${T}_{\mathrm{c}}.$ Partial substitution of Sr by Ln (Ln = La, Pr, Nd, Sm, Eu, Gd, and Bi) in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{1.6}{\mathrm{Ln}}_{0.4}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ results in a monotonic decrease of ${T}_{\mathrm{c}}$ with increasing ionic radius mismatch. By minimizing Sr site disorder at the expense of Ca site disorder, we demonstrate that the ${T}_{\mathrm{c}}$ of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ can be increased to 96 K. Based on these results we discuss the effects of chemical inhomogeneity in other bulk high-temperature superconductors.

/pdf/effect-of-chemical-inhomogeneity-in-bismuth-based-copper-2d70j9dsxt.pdf

Effect of chemical inhomogeneity in bismuth-based copper oxide superconductors

We have isolated a high-T/sub c/ phase in the Bi-Sr-Ca-Cu-O system of composition Bi/sub 4/(Sr,Ca)/sub 6/Cu/sub 4/O/sub 16/..mu../sub x/. The crystal substructure has a tetragonal unit cell (a = 3.817 A, c = 30.6 A) with similarities to both the oxygen-defect perovskites YBa/sub 2/Cu/sub 3/O/sub 7/..sqrt../sub x/ and the K/sub 2/NiF/sub 4/ structure of La/sub 2/CuO/sub 4/. The oxygen content, determined by titration and thermogravimetric analysis (TGA) experiments, corresponds to a formal oxidation state Cu(2.15). Oxygen can be reversibly depleted in an argon ambient in an amount corresponding to the reduction of the Cu(III) into Cu(II). The compound has a metalliclike resistance above its T/sub c/ near 85 K. Processing this precursor compound by heating to temperatures near its melting point (885 /sup 0/C) produces a sharp resistivity drop near 110 K that we show by ac susceptibility and Meissner effect is due to a superconducting transition.

/pdf/crystal-substructure-and-physical-properties-of-the-4hke8jvwar.pdf

Crystal substructure and physical properties of the superconducting phase Bi4(Sr,Cr)6Cu4O16+x.

Crystals of the three Bi-based cuprates of general formula ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{n\ensuremath{-}1}{\mathrm{Cu}}_{n}{\mathrm{O}}_{y}$ with $n=1,2, \mathrm{and} 3$ have been isolated and their structural and physical properties investigated. The structures are similar, differing only in the number of Cu${\mathrm{O}}_{2}$-Ca-Cu${\mathrm{O}}_{2}$ slabs packed along the $c$ axis. The insertion of one and two slabs increases $c$ from 24.6 to 30.6 and 37.1 \AA{}. Transmission electron microscopy shows there are stacking faults within the crystals in agreement with our x-ray data and its analysis. Resistivity, ac susceptibility, and dc magnetization measurements demonstrate superconductivity in the $n=1,2, \mathrm{and} 3$ phases at 10, 85, and 110 K, respectively. The observed transition temperatures and the stacking fault densities are dependent upon sample processing, in particular, the annealing temperatures and cooling rates. The transition temperature is, within the accuracy of our chemical titration, independent of the average copper valency that was determined to be 2.15 \ifmmode\pm\else\textpm\fi{} 0.03 for each of the three compounds.

/pdf/preparation-structure-and-properties-of-the-superconducting-ty7xj6g4jt.pdf

Preparation, structure, and properties of the superconducting compound series Bi 2 Sr 2 Ca n-1 Cu n O y with n=1, 2, and 3

The ${\mathrm{Bi}}_{4}$${\mathrm{Sr}}_{4}$${\mathrm{Ca}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{R}}_{\mathit{x}}$${\mathrm{Cu}}_{4}$${\mathrm{BO}}_{\mathit{y}}$ materials (R is a rare-earth element) were studied to determine their structural and physical properties. For most of the rare-earth elements, a complete solid solution exists up to x=2. Below x=0.5,${T}_{c}$ is not affected and for each added rare-earth element we find that about 0.5 oxygen atom is added to the structure. However, the structural modulation observed along the b axis for the undoped material persists and remains of the same amplitude for the rare-earth-doped samples. When more than one R(x\ensuremath{\ge}1) is substituted, ${T}_{c}$ is depressed and the compound becomes semiconducting beyond x=1.5. The depression in the ${T}_{c}$ from 85 K (x=0) to less than 4.2 K (x=1.5) correlates to a decrease in the formal valence of copper and is independent whether the rare-earth element is magnetic or nonmagnetic. No evidence for magnetic ordering over the range of temperature 1.7--400 K has been observed in all the substituted compounds. The substitution for Cu by 3d metals or for Sr by rare-earth elements fails for the 85-K Bi phase but succeeds for the 10-K Bi phase. Consequently, the following series ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{M}}_{\mathrm{x}}$${\mathrm{O}}_{\mathrm{y}}$ (M=Fe, Co) and ${\mathrm{Bi}}_{2}$${\mathrm{RCaCuO}}_{\mathrm{y}}$ (R=La, Pr, Nd, Sm) were made for study. These substitutions result in an uptake of oxygen (0.5 for each substituted element). But the materials become semiconducting even though the formal valence of Cu remains greater than 2. An antiferromagnetic transition at 140 K has been found for the Co sample for which Co is found to be in the +3 state.

/pdf/bismuth-cuprate-high-tc-superconductors-using-cationic-26mfftwlfz.pdf

Bismuth cuprate high-Tc superconductors using cationic substitution.

Superconducting critical transitions with an onset at 112 K and zero resistance at 107 K are obtained within the Bi-Sr-Ca-Cu-O system. The synthesis and formation of the 110-K superconducting phase using the 85-K material as a precursor is explained. The 110-K phase grows from the 85-K phase such that the resulting faceted crystal (a pseudomorph) can contain some of the 85-K phase in the core. With such a microstructure our magnetic data can be simply explained. A major structural difference between the 85- and 110-K materials is that the 85-K material can grow (relatively) large single crystals having long-range order whereas the 110-K material has only intermediate-range order (cryptocrystalline) of about 100--200 A.

/pdf/origin-of-the-110-k-superconducting-transition-in-the-bi-sr-4vjavaxky8.pdf

Origin of the 110-K superconducting transition in the Bi-Sr-Ca-Cu-O system.

The structure and magnetic properties of the Bi/sub 2/Sr/sub 2/Cu/sub 1/minus//ital x//M/sub x/O/sub /ital y// (/ital M/=Co and Fe) materials were studied. The limits of solid solution formation are at /ital x/=0.5 for the Fe system and /ital x/=1 for the Co system. Crystals of the new Bi/sub 2/Sr/sub 2/CoO/sub /ital Y// phase were grown and the structure established by x-ray crystallography. The subcell is the same as that of the 10-K superconductor, Bi/sub 2/Sr/sub 2/CuO/sub /ital y//, but the superstructure is different, as it exhibits a commensurate modulation of periodicity 4 instead of 5. Extra oxygen is accommodated in the Bi layers, as in Bi/sub 2/Sr/sub 3/Fe/sub 2/O/sub /ital y//, and the structure of the Bi-O layers can be described as 50% rocksalt-type and 50% oxygen-deficient perovskite for /ital x/=1, but with disorder at the oxygen positions. The formal valence of Co in this compound is about 2.5+-0.2 as deduced from structural and chemical measurements, whereas Fe adopts the oxidation state +3 as deduced by M/umlt o/ssbauer measurements. Bi/sub 2/Sr/sub 2/CoO/sub /ital y// is an antiferromagnetic insulator with the spins lying within the CoO/sub 2/ sheets and the antiferromagnetic ordering temperature (/ital T//sub /ital N//) is sensitive to processingmore » conditions and composition changes. The high anisotropy of the susceptibility suggests that Bi/sub 2/Sr/sub 2/CoO/sub /ital y// may be an Ising or /ital XY/ antiferromagnet.« less

/pdf/structure-and-magnetic-properties-of-nonsuperconducting-4zfeab174o.pdf

M. Giroud

Papers

Crystal substructure and physical properties of the superconducting phase Bi4(Sr,Cr)6Cu4O16+x.

Preparation, structure, and properties of the superconducting compound series Bi 2 Sr 2 Ca n-1 Cu n O y with n=1, 2, and 3

Bismuth cuprate high-Tc superconductors using cationic substitution.

Origin of the 110-K superconducting transition in the Bi-Sr-Ca-Cu-O system.

Structure and magnetic properties of nonsuperconducting doped Co and Fe Bi2Sr2Cu1-xMxOy phases.