Phenomenological model of nuclear relaxation in the normal state of YBa2Cu3O7.
TL;DR: A phenomenological model of a system of antiferromagnetically correlated spins is shown to give a good quantitative description of NMR, nuclear-quadrupole-resonance, and Knight-shift measurements on yttrium, planar copper, and planar oxygen sites in YBa{sub 2}Cu{sub 3}O{sub 7}.
Abstract: A phenomenological model of a system of antiferromagnetically correlated spins is shown to give a good quantitative description of NMR, nuclear-quadrupole-resonance, and Knight-shift measurements on yttrium, planar copper, and planar oxygen sites in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. The antiferromagnetic correlation length is estimated to be \ensuremath{\sim}2.5 lattice constants at T=100 K. The temperature dependence of the correlation length ceases at ${\mathit{T}}_{\mathit{x}}$\ensuremath{\simeq}100 K. The enhancement of the observed relaxation rates over what is expected for weakly interacting electrons is calculated and shown to be large. Extension of the calculation to other cuprate superconductors is discussed.
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TL;DR: The pseudogap is seen in all high-temperature superconductors and there is general agreement on the temperature and doping range where it exists as discussed by the authors, and it is also becoming clear that the superconducting gap emerges from the normal state pseudogaps.
Abstract: We present an experimental review of the nature of the pseudogap in the cuprate superconductors. Evidence from various experimental techniques points to a common phenomenology. The pseudogap is seen in all high-temperature superconductors and there is general agreement on the temperature and doping range where it exists. It is also becoming clear that the superconducting gap emerges from the normal state pseudogap. The d-wave nature of the order parameter holds for both the superconducting gap and the pseudogap. Although an extensive body of evidence is reviewed, a consensus on the origin of the pseudogap is as lacking as it is for the mechanism underlying high-temperature superconductivity.
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TL;DR: A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented in this article, where the effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered.
Abstract: A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented. Being semiconductors for one spin projection and metals for another, these substances are promising magnetic materials for applications in spintronics (i.e., spin-dependent electronics). Classification of HMFs by the peculiarities of their electronic structure and chemical bonding is discussed. The effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered. Special attention is paid to the appearance of nonquasiparticle states in the energy gap, which provide an instructive example of essentially many-body features in the electronic structure. State-of-the-art electronic calculations for correlated d-systems are discussed, and results for specific HMFs (Heusler alloys, zinc-blende structure compounds, CrO2, and Fe3O4) are reviewed.
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Cites methods from "Phenomenological model of nuclear r..."
...Usually the data on the longitudinal nuclear magnetic relaxation rate 1/T1 are discussed within itinerant-electron models such as Hubbard model or phenomenological spin-fluctuation theories (Ishigaki and Moriya, 1996; Millis et al., 1990; Moriya, 1985, 1994; Ueda and Moriya, 1975)....
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TL;DR: In this article, the authors review studies of the electromagnetic response of various classes of correlated electron materials including transition metal oxides, organic and molecular conductors, intermetallic compounds with $d$- and $f$-electrons as well as magnetic semiconductors.
Abstract: We review studies of the electromagnetic response of various classes of correlated electron materials including transition metal oxides, organic and molecular conductors, intermetallic compounds with $d$- and $f$-electrons as well as magnetic semiconductors. Optical inquiry into correlations in all these diverse systems is enabled by experimental access to the fundamental characteristics of an ensemble of electrons including their self-energy and kinetic energy. Steady-state spectroscopy carried out over a broad range of frequencies from microwaves to UV light and fast optics time-resolved techniques provide complimentary prospectives on correlations. Because the theoretical understanding of strong correlations is still evolving, the review is focused on the analysis of the universal trends that are emerging out of a large body of experimental data augmented where possible with insights from numerical studies.
668 citations
Cites background from "Phenomenological model of nuclear r..."
...…to the high-Tc pairing mechanism in the cuprates are divided in two main groups (Maier et al., 2008) (see Section V.A.1): According to the first school electrons form pairs due to a retarded attractive interaction mediated by virtual bosonic excitations in the solid (Millis et al., 1990)....
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TL;DR: In this article, the effects of finite temperature, primarily below T c, in a manner consistent with the BCS ground state wave function are investigated. But the authors focus on the intersection of two important problems: high T c superconductivity and superfluidity in ultracold fermionic atomic gases.
615 citations
Cites background from "Phenomenological model of nuclear r..."
...Initially, NMR measurements were interpreted as suggesting (Millis et al., 1990) strong antiferromagnetic fluctuations, while neutron measurements, which are generally viewed as the more conclusive, do not provide compelling evidence (Siet al., 1993) for their presence in the normal phase....
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