99 research outputs found
Unfolding spinor wavefunctions and expectation values of general operators: Introducing the unfolding-density operator
We show that the spectral weights used for the
unfolding of two-component spinor eigenstates can be decomposed as the sum of the
partial spectral weights calculated for each
component independently, effortlessly turning a possibly
complicated problem involving two coupled quantities into two independent
problems of easy solution. Furthermore, we define the unfolding-density
operator , which unfolds the
primitive cell expectation values of any
arbitrary operator according to
. As a proof of concept, we apply the method to
obtain the unfolded band structures, as well as the expectation values of the
Pauli spin matrices, for prototypical physical systems described by
two-component spinor eigenfunctions
Mott-Peierls Transition in the extended Peierls-Hubbard model
The one-dimensional extended Peierls-Hubbard model is studied at several band
fillings using the density matrix renormalization group method. Results show
that the ground state evolves from a Mott-Peierls insulator with a correlation
gap at half-filling to a soliton lattice with a small band gap away from
half-filling. It is also confirmed that the ground state of the Peierls-Hubbard
model undergoes a transition to a metallic state at finite doping. These
results show that electronic correlations effects should be taken into account
in theoretical studies of doped polyacetylene. They also show that a
Mott-Peierls theory could explain the insulator-metal transition observed in
this material.Comment: 4 pages with 3 embedded eps figure
Path Integral Description of a Semiclassical Su-Schrieffer-Heeger Model
The electron motion along a chain is described by a continuum version of the
Su-Schrieffer-Heeger Hamiltonian in which phonon fields and electronic
coordinates are mapped onto the time scale. The path integral formalism allows
us to derive the non local source action for the particle interacting with the
oscillators bath. The method can be applied for any value of the {\it e-ph}
coupling. The path integral dependence on the model parameters has been
analysed by computing the partition function and some thermodynamical
properties from up to room temperature. A peculiar upturn in the low
temperature {\it heat capacity over temperature} ratio (pointing to a glassy
like behavior) has been ascribed to the time dependent electronic hopping along
the chain
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