103 research outputs found
Resonant plasmon-phonon coupling and its role in magneto-thermoelectricity in bismuth
Using diagrammatic methods we derive an effective interaction between a low
energy collective movement of fermionic liquid (acoustic plasmon) and acoustic
phonon. We show that the coupling between the plasmon and the lattice has a
very non-trivial, resonant structure. When real and imaginary parts of the
acoustic plasmon's velocity are of the same order as the phonon's velocity, the
resonance qualitatively changes the nature of phonon-drag. In the following we
study how magneto-thermoelectric properties are affected. Our result suggests
that the novel mechanism of energy transfer between electron liquid and crystal
lattice can be behind the huge Nernst effect in bismuth.Comment: accepted in EPJB, to appear with a highligh
Phase diagram of hole doped two-leg Cu-O ladders
In the weak coupling limit, we establish the phase diagram of a two-leg
ladder with a unit cell containing both Cu and O atoms, as a function of
doping. We use bosonization and design a specific RG procedure to handle the
additional degrees of freedom. Significant differences are found with the
single orbital case; for purely repulsive interactions, a completely massless
quantum critical region is obtained at intermediate carrier concentrations
(well inside the bands) where the ground state consists of an incommensurate
pattern of orbital currents plus a spin density wave (SDW) structure.Comment: 4 pages, 2 figures, accepted to Phys. Rev. B, Rapid Com
Luttinger liquid theory of purple bronze in the charge regime
Molybdenum purple bronze LiMoO is an exceptional
material known to exhibit one dimensional (1D) properties for energies down to
a few meV. This fact seems to be well established both in experiments and in
band structure theory. We use the unusual, very 1-dimensional band dispersion
obtained in \emph{ab-initio} DFT-LMTO band calculations as our starting point
to study the physics emerging below 300meV. A dispersion perpendicular to the
main dispersive direction is obtained and investigated in detail. Based on
this, we derive an effective low energy theory within the Tomonaga Luttinger
liquid (TLL) framework. We estimate the strength of the possible interactions
and from this deduce the values of the TLL parameters for charge modes. Finally
we investigate possible instabilities of TLL by deriving renormalization group
(RG) equations which allow us to predict the size of potential gaps in the
spectrum. While instabilities strongly suppress each other, the
instabilities cooperate, which paves the way for a possible CDW at the lowest
energies. The aim of this work is to understand the experimental findings, in
particular the ones which are certainly lying within the 1D regime. We discuss
the validity of our 1D approach and further perspectives for the lower energy
phases.Comment: We wish to acknowledge financial support of MaNEP, SectionI
Spin rotational symmetry breaking by orbital current patterns in two-leg ladders.
We investigate the physical consequences of orbital current patterns (OCP) in
doped two-leg Cu-O Hubbard ladders. The internal symmetry of the pattern, in
the case of the ladder structure, differs slightly from that suggested so far
for cuprates. We focus on this OCP and look for measurable signatures of its
existence. We compute the magnetic field produced by the OCP at each lattice
site, and estimate its value in view of a possible experimental detection.
Using a renormalization group (RG) analysis, we determine the changes that are
caused by the SU(2) spin-rotational symmetry breaking which occurs when the OCP
is present in the ground state phase diagram. The most signifcant one is an
in-plane SDW gap opening in an otherwise critical phase, at intermediate
dopings. We estimate the value of this gap, give an analytic expression for the
correlation functions and examine some of the magnetic properties of this new
phase which can be revealed in measurements. We compute the conductance in the
presence of a single impurity, using an RG analysis. A discussion of the
various sources of SU(2) symmetry breaking underscores the specificity of the
OCP induced effects.Comment: 12 pages, 3 figures, submitted to PR
Collective excitations and low temperature transport properties of bismuth
We examine the influence of collective excitations on the transport
properties (resistivity, magneto- optical conductivity) for semimetals,
focusing on the case of bismuth. We show, using an RPA approximation, that the
properties of the system are drastically affected by the presence of an
acoustic plasmon mode, consequence of the presence of two types of carriers
(electrons and holes) in this system. We found a crossover temperature T*
separating two different regimes of transport. At high temperatures T > T* we
show that Baber scattering explains quantitatively the DC resistivity
experiments, while at low temperatures T < T* interactions of the carriers with
this collective mode lead to a T^5 behavior of the resistivity. We examine
other consequences of the presence of this mode, and in particular predict a
two plasmon edge feature in the magneto-optical conductivity. We compare our
results with the experimental findings on bismuth. We discuss the limitations
and extensions of our results beyond the RPA approximation, and examine the
case of other semimetals such as graphite or 1T-TiSe_2
Effects of thermal- and spin- fluctuations on the band structure of purple bronze LiMoO
The band structures of ordered and thermally disordered
LiMoO are calculated by use of ab-initio DFT-LMTO method. The
unusual, very 1-dimensional band dispersion obtained in previous band
calculations is confirmed for the ordered structure, and the overall band
structure agrees reasonably with existing photoemission data. Dispersion and
bandstructure perpendicular to the main dispersive direction is obtained. A
temperature dependent band broadening is calculated from configurations with
thermal disorder of the atomic positions within the unit cell. This leads a
band broadening of the two bands at the Fermi energy which can become
comparable to their energy separation. The bands are particularly sensitive to
in-plane movements of Mo sites far from the Li-sites, where the
density-of-states is highest. The latter fact makes the effect of Li vacancies
on the two bands relatively small. Spin-polarized band results for the ordered
structure show a surprisingly large exchange enhancement on the high DOS Mo
sites. Consequences for spin fluctuations associated with a cell doubling along
the conducting direction are discussed
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