3,212 research outputs found
Vibron-polaron critical localization in a finite size molecular nanowire
The small polaron theory is applied to describe the vibron dynamics in an
adsorbed nanowire with a special emphasis onto finite size effects. It is shown
that the finite size of the nanowire discriminates between side molecules and
core molecules which experience a different dressing mechanism. Moreover, the
inhomogeneous behavior of the polaron hopping constant is established and it is
shown that the core hopping constant depends on the lattice size. However, the
property of a lattice with translational invariance is recovered when the size
of the nanowire is greater than a critical value. Finally, it is pointed out
that these features yield the occurrence of high energy localized states which
both the nature and the number are summarized in a phase diagram in terms of
the relevant parameters of the problem (small polaron binding energy,
temperature, lattice size).Comment: 17 pages, 10 figure
We see what we are trained to see, or must we? Some personal lessons from a brush with kuru research
Bond-order modulated staggered flux phase for the model on the square lattice
Motivated by the observation of inhomogeneous patterns in some high-T
cuprate compounds, several variational Gutzwiller-projected wave-functions with
built-in charge and bond order parameters are proposed for the extended
model on the square lattice at low doping. First, following a recent
Gutzwiller-projected mean-field approach by one of us (Phys. Rev. B. {\bf 72},
060508(R) (2005)), we investigate, as a function of doping and Coulomb
repulsion, the stability of the staggered flux phase with respect to small
spontaneous modulations of squared unit cells ranging from to
. It is found that a bond-order (BO)
modulation appears spontaneously on top of the staggered flux pattern for hole
doping around 1/8. A related wave-function is then constructed and optimized
accurately and its properties studied extensively using an approximation-free
variational Monte Carlo scheme. Finally, the competition of the BO-modulated
staggered flux wave-function w.r.t. the d-wave RVB wave-function or the
commensurate flux state is investigated. It is found that a short range Coulomb
repulsion penalizes the d-wave superconductor and that a moderate Coulomb
repulsion brings them very close in energy. Our results are discussed in
connection to the STM observations in the under-doped regime of some cuprates.Comment: 10 pages, 9 figure
- âŠ