146 research outputs found
Spin, Orbital and Charge Order at the Interface between Correlated Oxides
The collective behavior of correlated electrons in the VOinterface layer
of LaVO/SrTiO heterostructure is studied within a quarter-filled
-orbital Hubbard model on a square lattice. We argue that the ground
state is ferromagnetic driven by the double exchange mechanism, and is
orbitally and charge ordered due to a confined geometry and electron
correlations. The orbital and charge density waves open gaps on the entire
Fermi surfaces of all orbitals. The theory explains the observed insulating
behavior of the -type interface between LaVO and SrTiO.Comment: 4 pages, 5 figures; revised, to appear in Phys. Rev. Let
Renormalization group approach to the one-dimensional 1/4-filled Hubbard model with alternating on-site interactions
The one-dimensional Hubbard model with different on-site interactions is
investigated by renormalization group technique. In the case of a 1/4-filled
band the dynamical nonequivalence of sites leads to the appearance of Umklapp
processes in the system and to the dynamical generation of a gap in the charge
excitation spectrum for , or . The
ground-state phase diagram is obtained in the limit of second order
renormalization. Depending on the sign and relative values of the bare coupling
constants, there is a gap in the spin or charge excitation spectrum and the
model system tends to superconducting or antiferromagnetic order at T=0, with
doubled period. The role of interaction between particles on nearest and
next-nearest neighbor sites is also considered
Ground state properties and excitation spectra of non-Galilean invariant interacting Bose systems
We study the ground state properties and the excitation spectrum of bosons
which, in addition to a short-range repulsive two body potential, interact
through the exchange of some dispersionless bosonic modes. The latter induces a
time dependent (retarded) boson-boson interaction which is attractive in the
static limit. Moreover the coupling with dispersionless modes introduces a
reference frame for the moving boson system and hence breaks the Galilean
invariance of this system. The ground state of such a system is depleted {\it
linearly} in the boson density due to the zero point fluctuations driven by the
retarded part of the interaction. Both quasiparticle (microscopic) and
compressional (macroscopic) sound velocities of the system are studied. The
microscopic sound velocity is calculated up the second order in the effective
two body interaction in a perturbative treatment, similar to that of Beliaev
for the dilute weakly interacting Bose gas. The hydrodynamic equations are used
to obtain the macroscopic sound velocity. We show that these velocities are
identical within our perturbative approach. We present analytical results for
them in terms of two dimensional parameters -- an effective interaction
strength and an adiabaticity parameter -- which characterize the system. We
find that due the presence of several competing effects, which determine the
speed of the sound of the system, three qualitatively different regimes can be
in principle realized in the parameter space and discuss them on physical
grounds.Comment: 6 pages, 2 figures, to appear in Phys. Rev.
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