Magnetic excitations in high temperature superconductors have been intensively studied experimentally and theoretically for a number of years as they provide a direct and incisive probe of correlation effects in the cuprates. These efforts have been redoubled after the discovery of a sharp magnetic collective mode in YBa2Cu3O7 by inelastic neutron scattering [1–3]. This mode is strongly coupled...

Magnetic excitations in high temperature superconductors have been intensively studied experimentally and theoretically for a number of years as they provide a direct and incisive probe of correlation effects in the cuprates. These efforts have been redoubled after the discovery of a sharp magnetic collective mode in YBa2CusOr by inelastic neutron scattering [1-3]. This mode is strongly coupled...

We show that in ultrasmall superconducting grains any concentration of magnetic impurities or infinitely small orbital effect of magnetic field leads to destruction of the hard gap in the tunneling density of states, and find analytically the exponential tail at low energies. Thus, the tunneling density of states exhibits the "soft gap" behavior. As the energy approaches zero, it vanishes linea...

One type of order that has been observed to compete with superconductivity in cuprates involves alternating charge and antiferromagnetic stripes. Recent neutron scattering studies indicate that the magnetic excitation spectrum of a stripe-ordered sample is very similar to that observed in superconducting samples. In fact, it now appears that there may be a universal magnetic spectrum for the cu...

Stimulated by the discovery of high-temperature superconductivity, the electronic structure of late 3d transition-metal oxides is presently one of the most extensively studied subjects in condensed matter physics. In this review, we hope to summarize the progress we have made and the problems we are facing. The emphasis of the review is on the latest angle-resolved photoemission studies that ha...

In this paper, we review the low energy electronic structure of the kinetic energy driven d-wave cuprate superconductors. We give a general description of the chargespin separation fermion-spin theory, where the constrained electron is decoupled as the gauge invariant dressed holon and spin. In particular, we show that under the decoupling scheme, the charge-spin separation fermion-spin represe...

We show that the superconducting energy gap 2Delta can be directly observed in phonon spectra, as predicted by recent theories. In addition, since each phonon probes the gap on only a small part of the Fermi surface, the gap anisotropy can be studied in detail. Our neutron scattering investigation of the anisotropic conventional superconductor YNi2B2C demonstrates this new application of phonon...