24 research outputs found
Transmission-electron-microscopy study of charge-stripe order in La(1.725)Sr(0.275)NiO(4)
We characterize the local structure and correlations of charge stripes in
La(1.725)Sr(0.275)NiO(4) using transmission-electron microscopy. We present
direct evidence that the stripe modulation is indeed one-dimensional within
each NiO(2) plane. Furthermore, we show that individual stripes tend to be
either site-centered or bond-centered, with a bias towards the former. The
spacing between stripes often fluctuates about the mean, contributing to a
certain degree of frustration of the approximate body-centered stacking along
the c-axis. These results confirm ideas inferred from previous
neutron-diffraction measurements on doped nickelates, and demonstrate that
charge-stripe order is quite different from the conventional concept of
charge-density-wave order.Comment: 5 pages, 6 figures, submitted to PR
DDW Order and its Role in the Phase Diagram of Extended Hubbard Models
We show in a mean-field calculation that phase diagrams remarkably similar to
those recently proposed for the cuprates arise in simple microscopic models of
interacting electrons near half-filling. The models are extended Hubbard models
with nearest neighbor interaction and correlated hopping. The underdoped region
of the phase diagram features density-wave (DDW) order. In a
certain regime of temperature and doping, DDW order coexists with
antiferromagnetic (AF) order. For larger doping, it coexists with
superconductivity (DSC). While phase diagrams of this form
are robust, they are not inevitable. For other reasonable values of the
coupling constants, drastically different phase diagrams are obtained. We
comment on implications for the cuprates.Comment: 7 pages, 3 figure
Dispersion of Ordered Stripe Phases in the Cuprates
A phase separation model is presented for the stripe phase of the cuprates,
which allows the doping dependence of the photoemission spectra to be
calculated. The idealized limit of a well-ordered array of magnetic and charged
stripes is analyzed, including effects of long-range Coulomb repulsion.
Remarkably, down to the limit of two-cell wide stripes, the dispersion can be
interpreted as essentially a superposition of the two end-phase dispersions,
with superposed minigaps associated with the lattice periodicity. The largest
minigap falls near the Fermi level; it can be enhanced by proximity to a (bulk)
Van Hove singularity. The calculated spectra are dominated by two features --
this charge stripe minigap plus the magnetic stripe Hubbard gap. There is a
strong correlation between these two features and the experimental
photoemission results of a two-peak dispersion in LaSrCuO, and
the peak-dip-hump spectra in BiSrCaCuO. The
differences are suggestive of the role of increasing stripe fluctuations. The
1/8 anomaly is associated with a quantum critical point, here expressed as a
percolation-like crossover. A model is proposed for the limiting minority
magnetic phase as an isolated two-leg ladder.Comment: 24 pages, 26 PS figure