37 research outputs found
Modeling Antiferromagnetic Phase in Iron Pnictides: Weakly Ordered State
We examine electronic states of antiferromagnetic phase in iron pnictides by
mean-field calculations of the optical conductivity. We find that a five-band
model exhibiting a small magnetic moment, inconsistent with the
first-principles calculations, reproduces well the excitation spectra
characterized by a multi-peak structure emerging below the N\'{e}el temperature
at low energy, together with an almost temperature-independent structure at
high energy. Investigating the interlayer magnetoresistance for this model, we
also predict its characteristic field dependence reflecting the Fermi surface
Fermi Arc of Metallic Diagonal Stripes in High Tc Cuprates
Spectral weight is investigated for metallic diagonal stripe state in two
dimensional Hubbard model, and Fermi arc observed by angle-resolved
photoemission spectroscopy on LSCO is discussed. The Fermi arc coming from the
mid-gap state of diagonal stripe appears near
and equivalent position in the reciprocal space, and the gap opens below the
mid-gap state. We show how these spectral weight structure depends on the
phasing of stripes, i.e., site-centered or bond-centered stripes.Comment: 4 figure
Fermi arc in doped high-Tc cuprates
We propose a -density wave induced by the spin-orbit coupling in the CuO
plane. The spectral function of high-temperature superconductors in the under
doped and lightly doped regions is calculated in order to explain the Fermi arc
spectra observed recently by angle-resolved photoemission spectroscopy. We take
into account the tilting of CuO octahedra as well as the on-site
Coulombrepulsive interaction; the tilted octahedra induce the staggered
transfer integral between orbitals and Cu orbitals, and
bring about nontrivial effects of spin-orbit coupling for the electrons in
the CuO plane. The spectral weight shows a peak at around (,) for
light doping and extends around this point forming an arc as the carrier
density increases, where the spectra for light doping grow continuously to be
the spectra in the optimally doped region. This behavior significantly agrees
with that of the angle-resolved photoemissionspectroscopy spectra. Furthermore,
the spin-orbit term and staggered transfer effectively induce a flux state, a
pseudo-gap with time-reversal symmetry breaking. We have a nodal metallic state
in the light-doping case since the pseudogap has a symmetry.Comment: 5 pages, 7 figure
High-Energy Spin Dynamics in LaSrNiO
We have mapped out the spin dynamics in a stripe-ordered nickelate,
LaSrNiO with , using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: eV \AA, very similar to the velocity in the undoped, insulating
parent compound, LaNiO. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high- cuprates.Comment: 4 figure
Pressure-induced phase transition and bi-polaronic sliding in a hole-doped Cu_2O_3 ladder system
We study a hole-doped two-leg ladder system including metal ions, oxygen, and
electron-lattice interaction, as a model for Sr_{14-x}Ca_xCu_{24}O_{41-\delta}.
Single- and bi-polaronic states at 1/4-hole doping are modeled as functions of
pressure by applying an unrestricted Hartree-Fock approximation to a multiband
Peierls-Hubbard Hamiltonian. We find evidence for a pressure-induced phase
transition between single-polaron and bi-polaron states. The electronic and
phononic excitations in those states, including distinctive local lattice
vibrational modes, are calculated by means of a direct-space Random Phase
approximation. Finally, as a function of pressure, we identify a transition
between site- and bond-centered bi-polarons, accompanied by a soft mode and a
low-energy charge-sliding mode. We suggest comparisons with available
experimented data
Vibrational edge modes in intrinsically heterogeneous doped transition metal oxides
By applying an unrestricted Hartree-Fock and a Random Phase approximations to
a multiband Peierls-Hubbard Hamiltonian, we study the phonon mode structure in
models of transition metal oxides in the presence of intrinsic nanoscale
inhomogeneities induced by hole doping. We identify low frequency
vibrational modes pinned to the sharp interfaces between regions of distinct
electronic structure (doped and undoped) and separated in frequency from the
band of extended phonons. A characteristic of these ``edge'' modes is that
their energy is essentially insensitive to the doping level. We discuss the
experimental manifestations of these modes in inelastic neutron scattering, and
also in spin and charge excitation spectra.Comment: 5 pages, 4 figure
Electron-phonon anomaly related to charge stripes: static stripe phase versus optimally-doped superconducting La1.85Sr0.15CuO4
Inelastic neutron scattering was used to study the Cu-O bond-stretching
vibrations in optimally doped La1.85Sr0.15CuO4 (Tc = 35 K) and in two other
cuprates showing static stripe order at low temperatures, i.e.
La1.48Nd0.4Sr0.12CuO4 and La1.875Ba0.125CuO4. All three compounds exhibit a
very similar phonon anomaly, which is not predicted by conventional band
theory. It is argued that the phonon anomaly reflects a coupling to charge
inhomogeneities in the form of stripes, which remain dynamic in superconducting
La1.85Sr0.15CuO4 down to the lowest temperatures. These results show that the
phonon effect indicating stripe formation is not restricted to a narrow region
of the phase diagram around the so-called 1/8 anomaly but occurs in optimally
doped samples as well.Comment: to appear in J. Low Temp. Phy
Spin dynamics in stripe-ordered La5/3Sr1/3NiO4
Polarized and unpolarized neutron inelastic scattering has been used to
measure the spin excitations in the spin-charge-ordered stripe phase of
La5/3Sr1/3NiO4. At high energies, sharp magnetic modes are observed
characteristic of a static stripe lattice. The energy spectrum is described
well by a linear spin wave model with intra- and inter-stripe exchange
interactions between neighbouring Ni spins given by J = 15 +/- 1.5 meV and J' =
7.5 +/- 1.5 meV respectively. A pronounced broadening of the magnetic
fluctuations in a band between 10 meV and 25 meV is suggestive of coupling to
collective motions of the stripe domain walls.Comment: ReVTeX 4, 4 pages inc. 4 Fig