Although the vast majority of high-$T_c$ cuprate superconductors are hole-doped, a small family of electron-doped compounds exists. Under investigated until recently, there has been tremendous recent progress in their characterization. A consistent view is being reached on a number of formerly contentious issues, such as their order parameter symmetry, phase diagram, and normal state electronic structure. Many other aspects have been revealed exhibiting both their similarities and differences with the hole-doped compounds. This review summarizes the current experimental status of these materials, with a goal to providing a snapshot of our current understanding of electron-doped cuprates. When possible we put our results in the context of the hole-doped compounds. We attempt to synthesize this information into a consistent view on a number of topics important to both this material class as well as the overall cuprate phenomenology including the phase diagram, the superconducting order parameter symmetry, phase separation, pseudogap effects, the role of competing orders, the spin-density wave mean-field description of the normal state, and electron-phonon coupling.

Progress and perspectives on electron-doped cuprates

Publisher Summary This chapter describes the symmetry aspects of the crystal field and the parametrization of the energy level scheme. It provides an overview of the experimental data of trivalent lanthanide ions doped into crystalline host matrices. The selection rules for induced electric dipole (ED) and magnetic dipole (MD) transitions for systems with even or odd numbers of f electrons in different site symmetries are presented. Methods for the assignment of crystal-field levels are discussed and the determination of phenomenological crystal-field parameters is described. Such a set of crystal-field parameters in combination with a suitable set of free-ion parameters allows calculating crystal-field energy levels and reconstructing the energy diagram of the 4fn configuration. In this way, it is not only possible to check the validity of the crystal-field model but also to get information about energy levels, which cannot be detected experimentally.

Chapter 155 Rationalization of crystal-field parametrization

The properties of green thermoluminescence (TL) and persistent luminescence of Lu2O3:Tb3+ and Lu2O3:Tb3+,Ca2+ materials sintered in vacuum at 1700 °C were investigated. The concentration of Tb vari...

Thermoluminescence and Kinetics of Persistent Luminescence of Vacuum-Sintered Tb3+-Doped and Tb3+,Ca2+-Codoped Lu2O3 Materials

The idea that the ratio E/D ≡ λ can be confined by a proper choice of the axis system to the range (0,±1/3) serves as a basis for the standardization of the spin Hamiltonian and the ligand field Hamiltonian for orthorhombic symmetry Due to recent results on the transformation of the Stevens operators Oqk, relations are given which allow for extension of the standardization to the spin Hamiltonian for paramagnetic centers with spin S≥2 Several EPR studies of 3dn and 4 f n ions in crystals are reconsidered The results prove the usefulness of the clear choice of the parameters Bqk suggested by the standardization idea Application of the standardization in the area of the ligand field theory, which seems rather novel, is also considered Crystal‐field parameters for several rare earth ions in garnets are recalculated An arbitrary choice from among the equivalent sets of the crystal‐field parameters used in the review by Morrison and Leavitt (1982) should be replaced by a transformation to the ‘‘standard’’ set

On standardization of the spin Hamiltonian and the ligand field Hamiltonian for orthorhombic symmetry

L'auto-extinction de Nd3+ : Son mecanisme fondamental et un critere predictif simple pour les materiaux minilaser

Valence of praseodymium in PrxY1-xBa2Cu3O7- delta : Inelastic-neutron-scattering, specific-heat, and susceptibility study.

We present an infrared transmission ${\mathrm{Pr}}^{3+}$ crystal-field study of as-grown, reduced, and oxygenated ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}}$ single crystals and thin films. Excitations from the ground-state multiplet ${}^{3}{\mathrm{H}}_{4}$ to the ${}^{3}{\mathrm{H}}_{5},$ ${}^{3}{\mathrm{H}}_{6},$ ${}^{3}{\mathrm{F}}_{2},$ and ${}^{3}{\mathrm{F}}_{3}$ excited multiplets are observed in all samples. In addition to the ${\mathrm{Pr}}^{3+}$ regular sites, which remain unperturbed following the cerium doping or the oxygen content modifications, ${\mathrm{Pr}}^{3+}$ sites are detected. A precise set of crystal-field parameters, which reproduces the energy and the symmetry of the levels, is determined. The reduction process, which drives the electron-doped cuprates superconducting, is discussed in detail and scenarios for the reduction mechanism and induced vacancies are proposed. In contrast to the common belief, the apical oxygen, which is clearly detected in all samples, is not removed in ${\mathrm{Pr}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4}$ following reduction. This observation questions the role attributed to the apical oxygen removal in triggering the superconductivity.

Pr 3 + crystal-field excitation study of apical oxygen and reduction processes in Pr 2 − x Ce x CuO 4 ± δ

A crystal field analysis of the reported optical spectra of Nd3+ in the series of aluminium and gallium garnets LuAG, YAG, GGG, LuGG, and YGG is presented. The reliability of the crystal field parameters determined in this way is confirmed by comparison with ESR g-values given in the literature. The results obtained represent a basis for a further study of the relation between the crystal field parameters of rare earths in garnets and the structure of the coordination dodecahedron.



[Russian Text Ignore]

The Crystal Field for Nd3+ in Garnets

We have observed Raman active ${\mathrm{Nd}}^{3+}$ crystal-field (CF) excitations as a function of temperature in reduced single crystals of ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$ The lines detected correspond to 13 different transitions involving crystal-field split levels of the (J=9/2) ground state as well as the higher excited multiplets with J=11/2, 13/2, and 15/2 Eight of these excitations have been measured out of resonance, thus allowing their symmetry to be determined Using these levels, we have calculated an unequivocal set of CF parameters, thus solving an outstanding controversy between different neutron measurements We conjecture that changes in the spectra measured on the reduced sample compared to the as-grown one result from the removal of apical oxygen

V. Nekvasil

Papers

Valence of praseodymium in PrxY1-xBa2Cu3O7- delta : Inelastic-neutron-scattering, specific-heat, and susceptibility study.

Pr 3 + crystal-field excitation study of apical oxygen and reduction processes in Pr 2 − x Ce x CuO 4 ± δ

The Crystal Field for Nd3+ in Garnets

Raman study of intermultiplet crystal-field excitations in Nd2CuO4.

Raman study of crystal-field excitations in nd1.85ce0.15cuo4