832 research outputs found
Solitons: from Charge Density Waves to FFLO in superconductors
This short review aims to summarize on "What the Charge Density Waves can
tell to other inhomogeneous states in strongly correlated systems, particularly
to spin-polarized superconductors". We shall update on expanding observations
of solitons in quasi 1D CDW conductors and link them to the growing information
and demands related to inhomogeneous spin-polarized states in superconductors.
The related theory, existent or awaited for, stretches from solitons in 1D
models to vortex-like elementary excitations in 2D,3D ordered incommensurate
CDWs and superconductors.Comment: After presentations given at the conferences STRIPES 2008 and ECRYS
200
Theory of the ferroelectric phase in organic conductors: optics and physics of solitons
Recently the ferroelectric anomaly (Nad, Monceau, et al) followed by the
charge disproportionation (Brown, et al) have been discovered in (TMTTF)2X
compounds. The corresponding theory of the combined Mott-Hubbard state
describes both effects by interference of the build-in nonequivalence of bonds
and the spontaneous one of sites. The state gives rise to three types of
solitons: \pi solitons (holons) are observed via the activation energy \Delta
in the conductivity ; noninteger \alpha solitons (the FE domain walls)
provide the frequency dispersion of the ferroelectric response; combined
spin-charge solitons determine G(T) below subsequent structural transitions of
the tetramerisation. The photoconductivity gap 2\Delta is determined by
creations of soliton - antisoliton pairs. The optical edge lies well below,
given by the collective ferroelectric mode which coexists with the combined
electron-phonon resonance and the phonon antiresonance. The charge
disproportionation and the ferroelectricity can exist hiddenly even in the Se
subfamily giving rise to the unexplained yet low frequency optical peak, the
enhanced pseudogap and traces of phonons activation.Comment: small fixe
Competing Interactions, the Renormalization Group and the Isotropic-Nematic Phase Transition
We discuss 2D systems with Ising symmetry and competing interactions at
different scales. In the framework of the Renormalization Group, we study the
effect of relevant quartic interactions. In addition to the usual constant
interaction term, we analyze the effect of quadrupole interactions in the self
consistent Hartree approximation. We show that in the case of repulsive
quadrupole interaction, there is a first order phase transition to a stripe
phase in agreement with the well known Brazovskii result. However, in the case
of attractive quadrupole interactions there is an isotropic-nematic second
order transition with higher critical temperature.Comment: 4 pages, no figures, version to be published in Physical Review
Letters. Some scaling dimensions corrected, conclusions are the sam
New Routes to Solitons in Quasi One-Dimensional Conductors
We collect evidences on existence of microscopic solitons, and their
determining role in electronic processes of quasi-1D conductors. The
ferroelectric charge ordering gives access to several types of solitons in
conductivity and permittivity, and to solitons' bound pairs in optics - both in
insulating and conducting cases of TMTTF and TMTSF subfamilies. The excursion
to physics of conjugated polymers allows to suggest further experiments.
Internal tunnelling in Charge Density Waves goes through the channel of
"amplitude solitons", which correspond to the long sought quasi-particle - the
spinon. The same experiment gives an access to the reversible reconstruction of
the junction via spontaneous creation of a lattice of 2Pi solitons - a grid of
dislocations. The individual 2Pi solitons have been visually captured in recent
STM experiments. Junctions of organic and oxide conductors are anticipated to
show similar effects of reconstruction.Comment: Proceedings of ISCOM 2007, to be published in Solid State Sciences
(2008
Inhomogeneous and nonstationary Hall states of the CDW with quantized normal carriers
We suggest a theory for a deformable and sliding charge density wave (CDW) in
the Hall bar geometry for the quantum limit when the carriers in remnant small
pockets are concentrated at lowest Landau levels (LL) forming a fractionally
() filled quantum Hall state. The gigantic polarizability of the CDW
allows for a strong redistribution of electronic densities up to a complete
charge segregation when all carriers occupy, with the maximum filling, a
fraction of the chain length - thus forming the integer quantum Hall
state, while leaving the fraction of the chain length unoccupied. The
electric field in charged regions easily exceeds the pinning threshold of the
CDW, then the depinning propagates into the nominally pinned central region via
sharp domain walls. Resulting picture is that of compensated collective and
normal pulsing counter-currents driven by the Hall voltage. This scenario is
illustrated by numerical modeling for nonstationary distributions of the
current and the electric field. This picture can interpret experiments in
mesa-junctions showing depinning by the Hall voltage and the generation of
voltage-controlled high frequency oscillations (Yu.I. Latyshev, P. Monceau,
A.A. Sinchenko, et al, presented at ECRYS-2011, unpublished).Comment: After International School - Workshop on Electronic Crystals:
ECRYS-201
Statistics of charged solitons and formation of stripes
The 2-fold degeneracy of the ground state of a quasi-one-dimensional system
allows it to support topological excitations such as solitons. We study the
combined effects of Coulomb interactions and confinement due to interchain
coupling on the statistics of such defects. We concentrate on a 2D case which
may correspond to monolayers of polyacetylene or other charge density waves.
The theory is developped by a mapping to the 2D Ising model with long-range
4-spin interactions. The phase diagram exhibits deconfined phases for liquids
and Wigner crystals of kinks and confined ones for bikinks. Also we find
aggregated phases with either infinite domain walls of kinks or finite rods of
bikinks. Roughening effects due to both temperature and Coulomb repulsion are
observed. Applications may concern the melting of stripes in doped correlated
materials.Comment: 16 pages, 7 figure
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