249 research outputs found
Ferroelectric Mott-Hubbard phase in organic conductors
We present key issues of related phenomenons of the Ferroelectricity and the
Charge Disproportionation in organic metals. In (TMTTF_2X the dielectric
susceptibility demonstrates clear cases of the ferroelectric and
anti-ferroelectric phase transitions. Both the susceptibility and the
conductivity prove independence and occasional coexistence of "structurless"
ferroelectric transitions and usual "anionic" ones. Their sequence gives access
to physics of three types of solitons emerging upon cooling via several steps
of symmetry breaking. The theory invokes a concept of the Combined Mott-Hubbard
State which focuses upon weak processes of electronic Umklapp scattering coming
from both the build-in nonequivalence of bonds and the spontaneous one of
sites. We propose that the charge ordering in its form of the ferroelectricity
exists hiddenly even in the Se subfamily (TMTSF)_2X, giving rise to the
unexplained yet low frequency optical peak and the enhanced pseudogap.Comment: Proceedings of the ICSM 200
The ferroelectric Mott-Hubbard phase of organic (TMTTF)2X conductors
We present experimental evidences for a ferro-electric transition in the
family of quasi one- dimensional conductors (TMTTF)2X. We interpret this new
transition in the frame of the combined Mott-Hubbard state taking into account
the double action of the spontaneous charge disproportionation on the TMTTF
molecular stacks and of the X anionic potentials
Torque and temperature dependence of the hysteretic voltage-induced torsional strain in tantalum trisulfide
We have measured the dependence of the hysteretic voltage-induced torsional
strain (VITS) in crystals of orthorhombic tantalum trisulfide on temperature
and applied torque. In particular, applying square-wave voltages above the
charge-density-wave (CDW) threshold voltage, so as to abruptly switch the
strain across its hysteresis loop, we have found that the time constant for the
VITS to switch (at different temperatures and voltages) varied as the CDW
current. Application of torque to the crystal could also change the VITS time
constant, magnitude, and sign, suggesting that the VITS is a consequence of
residual torsional strain in the sample which twist the CDW. Application of
voltage changes the pitch of these CDW twists, which then act back on the
lattice. However, it remains difficult to understand the sluggishness of the
response.Comment: 20 pages, including 7 figures, to be published in PR
Dielectric response of charge induced correlated state in the quasi-one-dimensional conductor (TMTTF)2PF6
Conductivity and permittivity of the quasi-one-dimensionsional organic
transfer salt (TMTTF)2PF6 have been measured at low frequencies (10^3-10^7 Hz)
between room temperature down to below the temperature of transition into the
spin-Peierls state. We interpret the huge real part of the dielectric
permittivity (up to 10^6) in the localized state as the realization in this
compound of a charge ordered state of Wigner crystal type due to long range
Coulomb interaction.Comment: 11 pages, 3 .eps figure
Critical dynamics and domain motion from permittivity of the electronic ferroelectric (TMTTF)2AsF6
The quasi one-dimensional organic conductor (TMTTF)2AsF6 shows the charge
ordering transition at Tc101K to a state of the ferroelectric Mott insulator
which is still well conducting. We present and interpret the experimental data
on the gigantic dielectric response in the vicinity of TCO, concentrating on
the frequency dependence of the inverse of the complex
permittivity . Surprisingly
for a ferroelectric, we could closely approach the 2nd order phase transition
and to deeply reach the critical dynamics of the polarization. We could analyse
the critical slowing-down when approaching Tc from both sides and to extract
the anomalous power law for the frequency dependence of the order parameter
viscosity. Moreover, below Tc we could extract a sharp absorption feature
coming from a motion of domain walls which shows up at a frequency well below
the relaxation rate.Comment: Proceedings of the international school-workshop on Electronic
Crystals: ECRYS-2014, Physica B (2014
Influence of the anion potential on the charge ordering in quasi-one dimensional charge transfer salts
We examine the various instabilities of quarter-filled strongly correlated
electronic chains in the presence of a coupling to the underlying lattice. To
mimic the physics of the (TMTTF)X Bechgaard-Fabre salts we also include
electrostatic effects of intercalated anions. We show that small displacements
of the anion can stabilize new mixed Charged Density Wave-Bond Order Wave
phases in which central symmetry centers are suppressed. This finding is
discussed in the context of recent experiments. We suggest that the recently
observed charge ordering is due to a cooperative effect between the Coulomb
interaction and the coupling of the electronic stacks to the anions. On the
other hand, the Spin-Peierls instability at lower temperature requires a
Peierls-like lattice coupling.Comment: Latex, 4 pages, 4 postscript figure
Electron-lattice coupling and the broken symmetries of the molecular salt (TMTTF)SbF
(TMTTF)SbF is known to undergo a charge ordering (CO) phase
transition at and another transition to an
antiferromagnetic (AF) state at . Applied pressure causes a
decrease in both and . When , the CO is largely
supressed, and there is no remaining signature of AF order. Instead, the ground
state is a singlet. In addition to establishing an expanded, general phase
diagram for the physics of TMTTF salts, we establish the role of
electron-lattice coupling in determining how the system evolves with pressure.Comment: 4 pages, 5 figure
Effect of nearest neighbor repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain
We have studied the influence of nearest-neighbor (NN) repulsion on the low
frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN
repulsion term induces the apparition of two new long range ordered phases (one
CDW for positive and one CDW for
negative ) that did not exist in the V=0 phase diagram. These results
are put into perspective with the newly observed charge ordered phases in
organic conductors and an interpretation of their origin in terms of
electron-molecular vibration coupling is suggested.Comment: 10 pages, 10 figure
Coexisting orders in the quarter-filled Hubbard chain with elastic deformations
The electronic properties of the quarter-filled extended
Peierls-Holstein-Hubbard model that includes lattice distortions and molecular
deformations are investigated theoretically using the bosonization approach. We
predict the existence of a wide variety of charge-elastic phases depending of
the values of the Peierls and Holstein couplings. We include the effect of the
Peierls deformation in the nearest-neighbor repulsion V, that may be present in
real materials where Coulomb interactions depend strongly on the distance, and
we show that the phase diagram changes substantially for large V when this term
is taken into account.Comment: 6 pages, 3 figure
Charge Ordering in the One-Dimensional Extended Hubbard Model: Implication to the TMTTF Family of Organic Conductors
We study the charge ordering (CO) in the one-dimensional (1D) extended
Hubbard model at quarter filling where the nearest-neighbor Coulomb repulsion
and dimerization in the hopping parameters are included. Using the cluster
mean-field approximation to take into account the effect of quantum
fluctuations, we determine the CO phase boundary of the model in the parameter
space at T=0 K. We thus find that the dimerization suppresses the stability of
the CO phase strongly, and in consequence, the realistic parameter values for
quasi-1D organic materials such as (TMTTF)PF are outside the region of
CO. We suggest that the long-range Coulomb interaction between the chains
should persist to stabilize the CO phase.Comment: 5 pages, 4 eps figures, to appear in 15 Nov. 2001 issue of PR
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