17,133 research outputs found

### Effective interactions and superconductivity in the t-J model in the large-N limit

The feasibility of a perturbation expansion for Green's functions of the t-J
model directly in terms of X-operators is demonstrated using the Baym- Kadanoff
functional method. As an application we derive explicit expressions for the
kernel of the linearized equation for the superconducting order parameter in
leading order of a 1/N expansion. The linearized equation is solved numerically
on a square lattice. We find that a reasonably strong instability occurs only
for even frequency pairing with d-wavelike symmetry. Results for the transition
temperature and the effective interaction are given as a function of doping.Comment: 31 pages, 11 figure

### ING4 (inhibitor of growth family, member 4)

Review on ING4 (inhibitor of growth family, member 4), with data on DNA, on the protein encoded, and where the gene is implicated

### C-Axis Tunneling Spectra in High-T$_c$ Superconductors in the Presence of a d Charge-Density Wave

The optimally doped and underdoped region of the $t-J$ model at large N (N is
the number of spin components) is governed by the competition of d-wave
superconductivity (SC) and a d Charge-Density Wave (d-CDW).The partial
destruction of the Fermi surface by the d-CDW and the resulting density of
states are discussed. Furthermore, c-axis conductances for incoherent and
coherent tunneling are calculated, considering both an isotropic and an
anisotropic in-plane momentum dependence of the hopping matrix element between
the planes. The influence of self-energy effects on the conductances is also
considered using a model where the electrons interact with a dispersionless,
low-lying branch of bosons. We show that available tunneling spectra from
break-junctions are best explained by assuming that they result from incoherent
tunneling with a strongly anisotropic hopping matrix element of the form
suggested by band structure calculations. The conductance spectra are then
characterized by one single peak which evolves continuously from the
superconducting to the d-CDW state with decreasing doping. The intrinsic c-axis
tunneling spectra are, on the other hand, best explained by coherent tunneling.
Calculated spectra show at low temperatures two peaks due to SC and d-CDW. With
increasing temperature the BCS-like peak moves to zero voltage and vanishes at
T$_c$,exactly as in experiment.Our results thus can explain why break junction
and intrinsic tunneling spectra are different from each other. Moreover, they
support a scenario of two competing order parameters in the underdoped region
of high-T$_c$ superconductors.Comment: 12 pages, 16 figure

### Superconductivity, d Charge-Density Wave and Electronic Raman Scattering in High-T$_c$ Superconductors

The competition of superconductivity and a d charge-density wave (CDW) is
studied in the t-J model as a function of temperature at large N where N is the
number of spin components. Applying the theory to electronic Raman scattering
the temperature dependence of the $B_{1g}$ and the $A_{1g}$ spectra are
discussed for a slightly underdoped case.Comment: 2 pages, 3 figures, Proc. M2S-HTSC-VII, to appear in Physica

### Electronic correlations, electron-phonon interaction, and isotope effect in high-Tc cuprates

Using a large-N expansion we present and solve the linearized equation for
the superconducting gap for a generalized t-J model which also contains phonons
within a Holstein model. The leading Tc has d-wave symmetry with phonons giving
a positive contribution to Tc. The corresponding isotope coefficient is very
small at optimal doping and increases towards the classical value 1/2 with
increasing dopings similar as in many cuprates.Comment: 14 pages, 7 figure

### Collective excitations in unconventional charge-density wave systems

The excitation spectrum of the t-J model is studied on a square lattice in
the large $N$ limit in a doping range where a $d$-$density$-$wave$ (DDW) forms
below a transition temperature $T^\star$. Characteristic features of the DDW
ground state are circulating currents which fluctuate above and condense into a
staggered flux state below $T^\star$ and density fluctuations where the
electron and the hole are localized at different sites. General expressions for
the density response are given both above and below $T^\star$ and applied to
Raman, X-ray, and neutron scattering. Numerical results show that the density
response is mainly collective in nature consisting of broad, dispersive
structures which transform into well-defined peaks mainly at small momentum
transfers. One way to detect these excitations is by inelastic neutron
scattering at small momentum transfers where the cross section (typically a few
per cents of that for spin scattering) is substantially enhanced, exhibits a
strong dependence on the direction of the transferred momentum and a
well-pronounced peak somewhat below twice the DDW gap. Scattering from the
DDW-induced Bragg peak is found to be weaker by two orders of magnitude
compared with the momentum-integrated inelastic part.Comment: 10 pages, 8 figure

### Influence of collective effects and the d-CDW on electronic Raman scattering in high-T$_c$ superconductors

Electronic Raman scattering in high-T$_c$ superconductors is studied within
the t-J model. It is shown that the A$_{1g}$ and B$_{1g}$ spectra are dominated
by amplitude fluctuations of the superconducting and the d-wave CDW order
parameters, respectively. The B$_{2g}$ spectrum contains no collective effects
and its broad peak reflects vaguely the doping dependence of T$_c$, similarly
to the pronounced peak in the A$_{1g}$ spectrum. The agreement of our theory
with the experiment supports the picture of two different, competing order
parameters in the underdoped regime of high-T$_c$ superconductors.Comment: 4 pages, 4 figures, will appear in PR

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