3,268 research outputs found
Stripe formation in electron-doped cuprates
We investigate the formation of charge domain walls in an electron-doped
extended Hubbard model for the superconducting cuprates. Within an unrestricted
Hartree-Fock approach, extended by the introduction of slave-bosons to obtain a
more proper treatment of strong correlations, we demonstrate the occurrence of
stripes in the (1,1) and (1,-1) directions having one doped electron per stripe
site. The different filling, direction and width of these electron-doped
stripes with respect to those obtained in the hole-doped systems have
interesting observable consequences, which are discussed.Comment: 4 pages, 2 encapsulated postscript figure
First-Order Pairing Transition and Single-Particle Spectral Function in the Attractive Hubbard Model
A Dynamical Mean Field Theory analysis of the attractive Hubbard model is
carried out. We focus on the normal state upon restricting to solutions where
superconducting order is not allowed. Nevertheless a clear first-order pairing
transition as a function of the coupling takes place at all the electron
densities out of half-filling. The transition occurs between a Fermi liquid,
stable for . The
spectral function in the Fermi liquid phase is constituted by a low energy
structure around the Fermi level (similar to the Kondo resonance of the
repulsive half-filled model), which disappears discontinuously at , and
two high energy features (lower and upper Hubbard bands), which persist in the
insulating phase.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Letter
Stabilization of A-type layered antiferromagnetic phase in LaMnO_3 by cooperative Jahn-Teller deformations
It is shown that the layered antiferromagnetic order in stoechiometric
LaMnO_3 cannot be understood purely from electronic interactions. On the
contrary, it mainly results from strong cooperative Jahn-Teller deformations.
Those involve a compression of the Mn-O octahedron along the c-axis (mode Q_3 <
0), while alternate Jahn-Teller deformations occur in the ab-plane (mode Q_2).
These deformations stabilize a certain type of orbital ordering. The resulting
superexchange couplings are calculated by exact diagonalization, taking into
account both e_g and t_{2g} orbitals. The main result is that antiferromagnetic
(ferromagnetic) coupling along the c-direction (ab-planes) can be understood
only if the Jahn-Teller energy is much larger than the superexchange couplings,
which is consistent with experiments. This mechanism contrasts with that based
on weak Jahn-Teller coupling which instead predicts elongation along the c-axis
(Q_3 > 0). The crucial role of the deformation anisotropy Q_2/Q_3 is also
emphasized.Comment: 8 pages, 6 figure
Electron-phonon interaction in Strongly Correlated Systems
The Hubbard-Holstein model is a simple model including both electron-phonon
interaction and electron-electron correlations. We review a body of theoretical
work investigating the effects of strong correlations on the electron-phonon
interaction. We focus on the regime, relevant to high-T_c superconductors, in
which the electron correlations are dominant. We find that the electron-phonon
interaction can still have important signatures, even if many anomalies appear,
and the overall effect is far from conventional. In particular in the
paramagnetic phase the effects of phonons are much reduced in the low-energy
properties, while the high-energy physics can be strongly affected by phonons.
Moreover, the electron-phonon interaction can still give rise to important
effects, like phase separation and charge-ordering, and it assumes a
predominance of forward scattering even if the bare interaction is assumed to
be local (momentum independent). Antiferromagnetic correlations reduce the
screening effects due to electron-electron interactions and revive the
electron-phonon effects.Comment: 15 pages, 12 figure
On localization effects in underdoped cuprates
We comment on transport experiments in underdoped LaSrCuO in the
non-superconducting phase. The temperature dependence of the resistance
strongly resembles what is expected from standard localization theory. However
this theory fails, when comparing with experiments in more detail.Comment: 8 pages, to be published in J. of Superconductivit
Intrinsic instability of electronic interfaces with strong Rashba coupling
We consider a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures, which includes a Rashba spin-orbit
coupling proportional to the electric field perpendicular to the interface.
Based on the standard mechanism of polarity catastrophe, we assume that the
electric field is proportional to the electron density. Under these simple and
general assumptions, we show that a phase separation instability occurs for
realistic values of the spin-orbit coupling and of the band parameters. This
could provide an intrinsic mechanism for the recently observed inhomogeneous
phases at the LaAlO_3/SrTiO_3 or LaTiO_3/SrTiO_3 interfaces.Comment: 5 pages, 4 figure
Odd parity charge density-wave scattering in cuprates
We investigate a model where superconducting electrons are coupled to a
frequency dependent charge-density wave (CDW) order parameter Delta(w). Our
approach can reconcile the simultaneous existence of low energy Bogoljubov
quasiparticles and high energy electronic order as observed in scanning
tunneling microscopy (STM) experiments. The theory accounts for the contrast
reversal in the STM spectra between positive and negative bias observed above
the pairing gap. An intrinsic relation between scattering rate and
inhomogeneities follows naturally.Comment: 5 pages, 3 figure
Jahn-Teller, Charge and Magnetic Ordering in half-doped Manganese Oxides
The phase diagram of half-doped manganite systems of formula
A_{0.5}A'_{0.5}MnO_3 is investigated within a single-orbital model
incorporating magnetic double-exchange and superexchange, together with
intersite Coulomb and electron-lattice interactions. Strong Jahn-Teller and
breathing mode deformations compete together and result in shear lattice
deformations. The latters stabilize the charge-ordered CE-type phase, which
undergo first-order transitions with temperature or magnetic field to either
Ferromagnetic metallic or Paramagnetic insulating phases. An essential feature
is the self-consistent screening of Coulomb and electron-phonon interactions in
the ferromagnetic phase.Comment: 10 pages, six figures (eps files) +two class file
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