3 research outputs found
Gap to Transition Temperature Ratio in Density Wave Ordering: a Dynamical Mean Field Study
We use the dynamical mean-field method to determine the origin of the large
ratio of the zero temperature gap to the transition temperature observed in
most charge density wave materials. The method is useful because it allows an
exact treatment of thermal fluctuations. We establish the relation of the
dynamical mean-field results to conventional diagrammatics and thereby
determine that in the physically relevant regime the origin of the large ratio
is a strong inelastic scattering.Comment: 4 figure
Infrared conductivity of a one-dimensional charge-ordered state: quantum lattice effects
The optical properties of the charge-ordering () phase of the
one-dimensional (1D) half-filled spinless Holstein model are derived at zero
temperature within a well-known variational approach improved including
second-order lattice fluctuations. Within the phase, the static lattice
distortions give rise to the optical interband gap, that broadens as the
strength of the electron-phonon () interaction increases. The lattice
fluctuation effects induce a long subgap tail in the infrared conductivity and
a wide band above the gap energy. The first term is due to the multi-phonon
emission by the charge carriers, the second to the interband transitions
accompanied by the multi-phonon scattering. The results show a good agreement
with experimental spectra.Comment: 5 figure
Infrared absorption of the charge-ordering phase: Lattice effects
The phase diagram of the half-filled spinless Holstein model for electrons
interacting with quantum phonons is derived in three dimensions extending at
finite temperature a variational approach introduced for the
one-dimensional T=0 case. Employing the variational scheme, the spectral and
optical properties of the system are evaluated in the different regimes that
characterize the normal and ordered state. The effects of the charge-ordering
() induce a transfer of spectral weight from low to high energies in the
conductivity spectra, as the temperature decreases or the strength of the
electron-phonon () interaction increases. The inclusion of effects of
lattice fluctuations is able to smooth the inverse square-root singularity
expected for the case of the mean-field approach and determines a subgap tail
absorption. Moreover, in the weak to intermediate coupling regime, a
two-component structure is obtained within the phase at low frequency: the
remnant Drude-like term and the incipient absorption band centered around the
gap energy.Comment: 8 figures. to appear on PR