Electronic Spectra and Their Relation to the (pi,pi) Collective Mode in High-Tc Superconductors

Recent laser angle-resolved photoemission spectroscopy studies have established the presence of a new kink in the low-energy nodal dispersion of Bi$_2$Sr$_2$CaCu$_2$O$+{8+\delta}$ (Bi-2212). The energy scale (~8-15 meV) of this kink appears below the maximum of the superconducting gap $\delta_0$. Therefore it is difficult to interpret this feature in terms of the usual coupling to a sharp dispersionless mode. In this paper we examine electron-phonon coupling to the in-plane a...

The energy gap for electronic excitations is one of the most important characteristics of the superconducting state, as it directly refects the pairing of electrons. In the copper-oxide high temperature superconductors (HTSCs), a strongly anisotropic energy gap, which vanishes along high symmetry directions, is a clear manifestation of the d-wave symmetry of the pairing. There is, however, a dramatic change in the form of the gap anisotropy with reduced carrier concentration ...

An angle resolved photoemission study on Ca2CuO2Cl2, a parent compound of high Tc superconductors is reported. Analysis of the electron occupation probability, n(k) from the spectra shows a steep drop in spectral intensity across a contour that is close to the Fermi surface predicted by the band calculation. This analysis reveals a Fermi surface remnant even though Ca2CuO2Cl2 is a Mott insulator. The lowest energy peak exhibits a dispersion with approximately the |cos(kxa)-co...

We use angle-resolved photoemission spectroscopy (ARPES) to investigate the properties of the energy gap(s) in optimally doped (Bi,Pb)2(Sr,La)2CuO6+d (Bi2201). We find that the spectral gap has two components in the superconducting state: a superconducting gap and pseudogap. Significant differences in their momentum and temperature dependence suggest that they represent two separate energy scales. Spectra near the node reveal a sharp peak with a small gap below Tc that closes...

We have used angular resolved photoemission to measure the angular dependence of the superconducting gap in highly overdoped Bi2212 (Tc=65K). While the node at 45 degrees is conserved, we find substantial deviation from a first order d-wave dependence away from the node. The pairing susceptibility is peaked at special regions on the Fermi surface. Comparing these results with a detailed mapping of the Fermi surface we performed, we could measure the extension and location of ...

We explain recent experimental results on the superconducting state spectral function as obtained by angle resolved photoemission, as well as by tunneling, in high Tc cuprates. In our model, electrons are coupled to the resonant spin fluctuation mode observed in inelastic neutron scattering experiments, as well as to a gapped continuum. We show that, although the weight of the resonance is small, its effect on the electron self energy is large, and can explain various dispers...

We present a phenomenological model that describes the low energy electronic structure of the cuprate high temperature superconductor Bi2Sr2CaCu2O8+x as observed by Spectroscopic Imagining Scanning Tunneling Microscopy (SI-STM). Our model is based on observations from Quasiparticle Interference (QPI) measurements and Local Density of States (LDOS) measurements that span a range of hole densities from critical doping, p~0.19, to extremely underdoped, p~0.06. The model presente...

Formation of electron pairs is essential to superconductivity. For conventional superconductors, tunnelling spectroscopy has established that pairing is mediated by bosonic modes (phonons); a peak in the second derivative of tunnel current d2I/dV2 corresponds to each phonon mode . For high-transition-temperature (high-Tc) superconductivity, however, no boson mediating electron pairing has been identified. One explanation could be that electron pair formation and related elect...

We study the electronic structure of Ca2-xNaxCuO2Cl2 and Bi2Sr2CaCu2O8+d samples in a wide range of doping, using angle-resolved photoemission spectroscopy, with emphasis on on the Fermi surface (FS) in the near anti-nodal region. The "nesting wave vector", i.e., the wave vector that connects two nearly flat pieces of the Fermi surface in the anti-nodal region, reveals a universal monotonic decrease in magnitude as a function of doping. Comparing our results to the charge ord...

Using an energy-momentum dispersion for Bi2Sr2CaCu2O8 obtained from angle-resolved photoelectron spectroscopy we show that the shrinking Fermi arc model of the pseudogap is inconsistent with Raman scattering below Tc and specific heat near T*. By simulating the quasiparticle energy dispersion curves we show that Fermi arcs are an artifact of a T-dependent scattering rate.