5,183 research outputs found

### Angle-resolved photoemission spectra in the cuprates from the d-density wave theory

Angle-resolved photoemission spectra present two challenges for the d-density
wave (DDW) theory of the pseudogap state of the cuprates: (1) hole pockets near
$(\pi/2,\pi/2)$ are not observed, in apparent contradiction with the assumption
of translational symmetry breaking, and (2) there are no well-defined
quasiparticles at the {\it antinodal} points, in contradiction with the
predictions of mean-field theory of this broken symmetry state. Here, we show
how these puzzles can be resolved.Comment: 4 pages, 3 eps figures, RevTex

### Spin-spin Correlation lengths of Bilayer Antiferromagnets

The spin-spin correlation length and the static structure factor for bilayer
antiferromagnets, such as YBa$_2$Cu$_3$O$_{6}$, are calculated using field
theoretical and numerical methods. It is shown that these quantities can be
directly measured in neutron scattering experiments using energy integrated
two-axis scan despite the strong intensity modulation perpendicular to the
layers. Our calculations show that the correlation length of the bilayer
antiferromagnet diverges considerably more rapidly, as the temperature tends to
zero, than the correlation length of the corresponding single layer
antiferromagnet typified by La$_2$CuO$_4$. This rapid divergence may have
important consequences with respect to magnetic fluctuations of the doped
superconductors.Comment: This paper supersedes cond-mat/9703138 and contains numerical
simulation results to compare against analytical results. 6 pages, 2
postscript figures (embedded), uses EuroPhys.sty and EuroMac

### Spectral Anomaly and High Temperature Superconductors

Spectral anomaly for interacting Fermions is characterized by the spectral
function $A([k-k_F],\omega)$ satisfying the scaling relation $A(\Lambda^{y_1}
[k-k_F],\Lambda^{y_2}\omega)= \Lambda^{y_A}A([k-k_F],\omega)$, where $y_1$,
$y_2$, and $y_A$ are the exponents defining the universality class. For a Fermi
liquid $y_1=1$, $y_2=1$, $y_A=-1$; all other values of the exponents are termed
anomalous. In this paper, an example for which $y_1=1$, $y_2=1$, but
$y_A=\alpha-1$ is considered in detail. Attractive interaction added to such a
critical system leads to a novel superconducting state, which is explored and
its relevance to high temperature cuprate superconductors is discussed.Comment: RevTex, 53 pages (including figures

### Superconductivity in hole-doped C60 from electronic correlations

We derive a model for the highest occupied molecular orbital band of a C60
crystal which includes on-site electron-electron interactions. The form of the
interactions are based on the icosahedral symmetry of the C60 molecule together
with a perturbative treatment of an isolated C60 molecule. Using this model we
do a mean-field calculation in two dimensions on the [100] surface of the
crystal. Due to the multi-band nature we find that electron-electron
interactions can have a profound effect on the density of states as a function
of doping. The doping dependence of the transition temperature can then be
qualitatively different from that expected from simple BCS theory based on the
density of states from band structure calculations

### On the ground state of metallic hydrogen

A proposed liquid ground state of metallic hydrogen at zero temperature is explored and a variational upper bound to the ground state energy is calculated. The possibility that the metallic hydrogen is a liquid around the metastable point (rs = 1.64) cannot be ruled out. This conclusion crucially hinges on the contribution to the energy arising from the third order in the electron-proton interaction which is shown here to be more significant in the liquid phase than in crystals

### An explanation for a universality of transition temperatures in families of copper oxide superconductors

A remarkable mystery of the copper oxide high-transition-temperature (Tc)
superconductors is the dependence of Tc on the number of CuO2 layers, n, in the
unit cell of a crystal. In a given family of these superconductors, Tc rises
with the number of layers, reaching a peak at n=3, and then declines: the
result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is
still poorly understood and attention has instead been mainly focused on the
properties of a single CuO2 plane. Here we show that the quantum tunnelling of
Cooper pairs between the layers simply and naturally explains the experimental
results, when combined with the recently quantified charge imbalance of the
layers and the latest notion of a competing order nucleated by this charge
imbalance that suppresses superconductivity. We calculate the bell-shaped curve
and show that, if materials can be engineered so as to minimize the charge
imbalance as n increases, Tc can be raised further.Comment: 15 pages, 3 figures. The version published in Natur

### The effects of magnetic field on the d-density wave order in the cuprates

We consider the effects of a perpendicular magnetic field on the d-density
wave order and conclude that if the pseudogap phase in the cuprates is due to
this order, then it is highly insensitive to the magnetic field in the
underdoped regime, while its sensitivity increases as the gap vanishes in the
overdoped regime. This appears to be consistent with the available experiments
and can be tested further in neutron scattering experiments. We also
investigate the nature of the de Haas- van Alphen effect in the ordered state
and discuss the possibility of observing it.Comment: 5 pages, 4 eps figures, RevTex4. Corrected a silly but important typo
in the abstrac

### Quantum oscillations in $\mathrm{YBa_{2}Cu_{3}O_{6+\delta}}$ from an incommensurate $d$-density wave order

We consider quantum oscillation experiments in
$\mathrm{YBa_{2}Cu_{3}O_{6+\delta}}$ from the perspective of an incommensurate
Fermi surface reconstruction using an exact transfer matrix method and the
Pichard-Landauer formula for the conductivity. The specific density wave order
considered is a period-8 $d$-density wave in which the current density is
unidirectionally modulated. The current modulation is also naturally
accompanied by a period-4 site charge modulation in the same direction, which
is consistent with recent magnetic resonance measurements. In principle Landau
theory also allows for a period-4 bond charge modulation, which is not
discussed, but should be simple to incorporate in the future. This scenario
leads to a natural, but not a unique, explanation of why only oscillations from
a single electron pocket is observed, and a hole pocket of roughly twice the
frequency as dictated by two-fold commensurate order, and the corresponding
Luttinger sum rule, is not observed. However, it is possible that even higher
magnetic fields will reveal a hole pocket of half the frequency of the electron
pocket or smaller. This may be at the borderline of achievable high field
measurements because at least a few complete oscillations have to be clearly
resolved.Comment: 8 pages, 7 figure

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