4,761 research outputs found
Electron Self-Energy of High Temperature Superconductors as Revealed by Angle Resolved Photoemission
In this paper, we review some of the work our group has done in the past few
years to obtain the electron self-energy of high temperature superconductors by
analysis of angle-resolved photoemission data. We focus on three examples which
have revealed: (1) a d-wave superconducting gap, (2) a collective mode in the
superconducting state, and (3) pairing correlations in the pseudogap phase. In
each case, although a novel result is obtained which captures the essense of
the data, the conventional physics used leads to an incomplete picture. This
indicates that new physics needs to be developed to obtain a proper
understanding of these materials.Comment: 5 pages, revtex, 3 encapsulated postscript figures, SNS97 proceeding
Evolution of the pairing pseudogap in the spectral function with interplane anisotropy
We study the pairing pseudogap in the spectral function as a function of
interplane coupling. The analytical expressions for the self-energy in the
critical regime are obtained for any degree of anisotropy. The frequency
dependence of the self-energy is found to be qualitatively different in two and
three dimensions, and the crossover from two to three dimensional behavior is
discussed. In particular, by considering the anisotropy of the Fermi velocity
and gap along the Fermi surface, we can qualitatively explain recent
photoemission experiments on high temperature superconductors concerning the
temperature dependent Fermi arcs seen in the pseudogap phase.Comment: 20 pages, revtex, 5 encapsulated postscript figures include
Fourier transform spectroscopy of d-wave quasiparticles in the presence of atomic scale pairing disorder
The local density of states power spectrum of optimally doped
BiSrCaCuO (BSCCO) has been interpreted in terms of
quasiparticle interference peaks corresponding to an "octet'' of scattering
wave vectors connecting k-points where the density of states is maximal. Until
now, theoretical treatments have not been able to reproduce the experimentally
observed weights and widths of these "octet'' peaks; in particular, the
predominance of the dispersing "q'' peak parallel to the Cu-O bond
directions has remained a mystery. In addition, such theories predict
"background'' features which are not observed experimentally. Here, we show
that most of the discrepancies can be resolved when a realistic model for the
out-of-plane disorder in BSCCO is used. Weak extended potential scatterers,
which are assumed to represent cation disorder, suppress large-momentum
features and broaden the low-energy "q''-peaks, whereas scattering at order
parameter variations, possibly caused by a dopant-modulated pair interaction
around interstitial oxygens, strongly enhances the dispersing "q''-peaks.Comment: 7 pages, 3 figure
Heat Transport and the Nature of the Order Parameter in Superconducting
Recent thermal conductivity data on the heavy fermion superconductor
have been interpreted as offering support for an model of the order
parameter as opposed to an model. In this paper, we analyze this issue
from a theoretical standpoint including the detailed effects of Fermi surface
and gap anisotropy. Our conclusion is that although current data put strong
constraints on the gap anisotropy, they cannot definitively distinguish between
these two models. Measurements on samples of varying quality could be decisive
in this regard, however.Comment: 8 pages, revtex, 15 uunencoded postscript figure
Staggered local density-of-states around the vortex in underdoped cuprates
We have studied a single vortex with the staggered flux (SF) core based on
the SU(2) slave-boson theory of high superconductors. We find that
whereas the center in the vortex core is a SF state, as one moves away from the
core center, a correlated staggered modulation of the hopping amplitude
and pairing amplitude becomes predominant. We predict that in this
region, the local density-of-states (LDOS) exhibits staggered modulation when
measured on the bonds, which may be directly detected by STM experiments.Comment: 4 pages, 3 figure
Truncation of a 2-dimensional Fermi surface due to quasiparticle gap formation at the saddle points
We study a two-dimensional Fermi liquid with a Fermi surface containing the
saddle points and . Including Cooper and Peierls channel
contributions leads to a one-loop renormalization group flow to strong coupling
for short range repulsive interactions. In a certain parameter range the
characteristics of the fixed point, opening of a spin and charge gap and
dominant pairing correlations are similar to those of a 2-leg ladder at
half-filling. An increase of the electron density we argue leads to a
truncation of the Fermi surface with only 4 disconnected arcs remaining.Comment: Reference added. RevTeX 4 pages incl. 4 ps file
Superconducting Gap Anisotropy and Quasiparticle Interactions: a Doping Dependent ARPES Study
Comparing ARPES measurements on Bi2212 with penetration depth data, we show
that a description of the nodal excitations of the d-wave superconducting state
in terms of non-interacting quasiparticles is inadequate, and we estimate the
magnitude and doping dependence of the Landau interaction parameter which
renormalizes the linear T contribution to the superfluid density. Furthermore,
although consistent with d-wave symmetry, the gap with underdoping cannot be
fit by the simple coskx-cosky form, which suggests an increasing importance of
long range interactions as the insulator is approached.Comment: 4 pages, 3 eps figs, manuscript and Fig. 3 significantly revise
Spin Pseudo Gap in La2-xSrxCuO4 Studied by Neutron Scattering
Spin excitations of La2-xSrxCuO have been studied using inelastic neutron
scattering techniques in the energy range of 2 meV =< w =< 12 meV and the
temperature range of 8 K =< T =< 150 K. We observed a signature of a spin
pseudo gap in the excitation spectrum above Tc for the slightly overdoped
sample with x = 0.18. On heating, the spin pseudo gap gradually collapses
between T = 80 K and 150 K. For the x = 0.15 and 0.20, although the visibility
of gap-like structure at T ~ Tc is lower compared to the x = 0.18 sample, the
broad bump of kai"(w) appears at w ~ 5 meV,close to the spin-gap energy at base
temperature, suggests the existence of the spin pseudo gap in the normal state.Comment: revtex, 7 pages, 8 eps figures, PRB (2003) in pres
Signature of the staggered flux state around a superconducting vortex in underdoped cuprates
Based on the SU(2) lattice gauge theory formulation of the t-J model, we
discuss possible signature of the unit cell doubling associated with the
staggered flux (SF) state in the lightly doped spin liquid. Although the SF
state appears only dynamically in a uniform d-wave superconducting (SC) state,
a topological defect [SU(2) vortex] freezes the SF state inside the vortex
core. Consequently, the unit cell doubling shows up in the hopping
() and pairing () order parameters of physical
electrons. We find that whereas the center in the vortex core is a SF state, as
one moves away from the core center, a correlated staggered modulation of
and becomes predominant. We predict that over the
region outside the core and inside the internal gauge field penetration depth
around a vortex center, the local density-of-states (LDOS) exhibits staggered
peak-dip (SPD) structure inside the V-shaped profile when measured on the
bonds. The SPD structure has its direct origin in the unit cell doubling
associated with the SF core and the robust topological texture, which has
little to do with the symmetry of the d-wave order parameter. Therefore the
structure may survive the tunneling matrix element effects and easily be
detected by STM experiment.Comment: 27 pages, 14 figures in GIF format, typo correcte
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