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We report an investigation at the endpoint region of the spin density wave state in (TMTSF) 2 PF 6 where metal and superconductivity emerge. Thanks to resistivity measurements along the three main crystallographic directions, we are able to follow the texture in this phase coexistence regime. In this respect, superconductivity is used as a decoration technique of the metallic pattern. We show that metal (superconductivity) emerges first along the c ⁎ direction in a counterintuitive manner. Then metal (superconductivity) domains evolves from filaments along the c ⁎ axis towards slabs perpendicular to the a -axis which melt together in the homogeneous phase at high pressure. This evolution is compatible with the proposition of the formation of a soliton phase in the vicinity of the critical pressure of the (TMTSF) 2 PF 6 phase diagram. more...

We report on studies of stationary states and their transient dynamic for an incommensurate charge density wave (ICDW) in a restricted geometry of two spatial dimensions. The model takes into account multiple fields in mutual nonlinear interactions: the amplitude and the phase of the complex order parameter, and distributions of the electric and chemical potentials, of the density and the current of normal carriers. We observed spontaneous formation of vortices (the ICDW dislocations), and followed events of their creation and the subsequent evolution. The vortices appear when the voltage across, or the current through, the sample exceed a threshold. The number of vortices remnant in the reconstructed stationary state increases stepwise – in agreement with experiments, while a much greater number of vortices appears during the intermediate transient states. The vortex core concentrates the electric dipole leading to sharp drops of the electric and chemical potentials across the core. That can lead to enhanced inter-layer tunneling making the core to be a self-tuned microscopic tunneling junction. The results are applied to experiments on nano-fabricated mesa-junctions. They also appeal to modern efforts of the field-effect transformations in correlated electronic systems. more...

We present results of non-linear magneto resistance (MR) of polyacetylene nanofibers in high magnetic field up to H = 30 T at low temperature T = 1.5 K. The MR was proven to be of the spin origin; it reaches 16% at highest H . Unexpectedly, the MR was suppressed by increasing electric field E , vanishing at E ≳ 5 × 10 4 V/cm. It is understood that the doping induced spinless charged soliton pairs, which are initially confined to a certain distance because of the interchain phase correlations, and are deconfined in high electric fields, resulting in a vanishing magneto resistance (VMR). The role of the specific, degenerate ground state of the polyacetylene is confirmed by parallel studies of the different magneto resistances of polyaniline nanofibers which contrarily is not affected by the electric field. more...

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., Proceedings of ISCOM 2007, to be published in Solid State Sciences (2008) more...

Victor Emery made seminal contributions to the theory of one-dimensional electronic systems and to its applications to organic metals. His inventions became illuminated recently when the joint effect of the ferroelectricity and the charge disproportionation has been discovered in (TMTTF)2X compounds and beyond. Several of his contributions came to agenda at once: separate gaps in spin/charge channels and the route to solitons, 4kF anomaly, dimerization gap, role of ionic transitions. New phenomena unify an unusual variety of concepts: ferroelectricity of good conductors, structural instability towards Mott-Hubbard state, Wigner crystallization in a dense electronic system, ordered 4kF density wave, richness of physics of solitons, interplay of structural and electronic symmetries. The ferroelectric state gives rise to several types of solitons carrying the electron charge, a noninteger charge, spin or both the spin and the charge in special cases. They are clearly observed via conductivity, electric and magnetic susceptibilities. Solitons are challenging for optics where they already seem to determine the pseudogap in absorption. Various features also appear, or are expected, from collective electronic and coupled electron-phonon modes. The last topic, as well as some aspects of physics of solitons, recalls also the contributions of M.J. Rice. Moreover, the observation of Mott-Hubbard states refers to classical results of A.A. Ovchinnikov., To be published in Synthetic Metals: proceedings of ICSM-04, the session in memory of V.J. Emery, M.J. Rice and A.A. Ovchinnikov. More information is available via presentations deposited at http://ipnweb.in2p3.fr/~lptms/membres/brazov/seminars.html more...

Conducting polymers can be considered as one-dimensional semiconductors with features of strongly correlated electronic systems. We can distinguish a large distance motion, governed by long range Coulomb interactions, and intra-molecular electronic correlations. We exploit the dielectric screening to go beyond the single chain picture and to compare excitons for polymers in solutions and in films. Our approach allows to connect such different questions as shallow singlet and deep triplet excitons in phenylenes, A g – B u exciton levels crossing in polyenes, common 1/ N energy dependencies in oligomers. For the fundamental edge structure we describe the suppression of DOS singularity by the long range Coulomb interactions in final state of e–h pair. more...

We review the solid state physics approach to electronic and optical properties of conducting polymers also with attempts to bring together languages of the solid state theory for polymers and the quantum chemistry of oligomers. We consider polymers as generic one-dimensional semiconductors with features of strongly correlated electronic systems. Our model combines the long range electron–hole Coulomb attraction with a specific effect of strong intra-monomer electronic correlations, which results in effective intra-monomer electron–hole repulsion. We explain, exploit and organize various experimental and numerical findings. For example we connect such different questions as shallow singlet and deep triplet excitons in phenylenes, A g –B u exciton levels crossing in polyenes, common 1/ N energy dependencies in oligomers. more...

We describe effects of the long-range Coulomb interactions on absorption and photoconductivity of polymeric semiconductors. The final-state interaction suppresses the 1D edge singularity of band-to-band transitions, reducing it to the final value. This value meets the averaged subgap absorption through the high excitonic series below the gap. After a dip, the absorption increases at the primary exciton peak. At moderately strong electric fields, higher excited states are destroyed, while the primary one is preserved. Our results explain the rounding of the e–h absorption edge observed in various polymeric semiconductors. Moreover, they quantitatively agree with new photoconductivity data on PPV-type polymers where new spectral features appear under electric field. more...

We review approach of the solid state physics to the electronic and optical properties of conducting polymers. We consider their generic features as 1D semiconductors as well as the particularities of the phenyl group. We are taking efforts to bring together the solid state theory for polymers and the quantum chemistry of oligomers. more...

The phase gradient in a sliding-charge density wave (CDW), which is observable as a longitudinal shift, q ∝∂ φ /∂ x , of the CDW satellite peak position, is due to the conversion free-electrons↔CDW-condensate, at the current electrodes. Using high resolution X-ray scattering techniques and time-resolved techniques, we monitor, on thin NbSe 3 whiskers, the shift, q ( x ), and its relaxation, q ( t ), upon switching off the current. more...

Phase slippage is required at the current electrodes of quasi-one-dimensional conductors with a charge density wave (CDW) ground state for the conversion from free to condensed carriers. We have performed at the ESRF high-resolution X-ray measurements of the spatially varying shift q(x) of the CDW satellite wave vector between current contacts on a thin NbSe 3 whisker in the sliding state. Applying direct currents, we observe at 90 K a steep exponential decrease of the shift within a few hundred microns from the contact. The CDW strain pro"le q(x )r e#ects the carrier conversion process, via nucleation and growth of phase-dislocation loops. Pulsed current measurements of the shift q show important di!erences between pulsed and dc current data, revealing a spatially dependent relaxational behaviour of the CDW strain. Using time-resolved high spatial resolution X-ray we observe at 300 lm from the electrode a stretched exponential-type decay of the shift q(t) upon switching o! the current („"75 K): q(t)"q 0 [exp(!t/q)k] with q"23 ms and k"0.36. ( 2000 Elsevier Science B.V. All rights reserved. more...

Ferroelectricity is one of the demanded effects in fundamental and applied solid state physics. Till now, the ferroelectrics were available mostly in the inorganic world. The breakthrough of 2000s was an unexpected discovery of the ferroelectricity related to the charge ordering in quasi-1D organic conductors (TMTTF)2X, and in some layered compounds. The achieved understanding of underlying mechanisms allows to speculate on synthesis of a would-be ferroelectric polymer: it must possess a combination of dimerizations of sites and bonds, one of which must be build-in and another spontaneous. The theory of these “combined Peierls states” predicts an existence of solitons (dimerization kinks) with non-integer variable charges—they are the walls separating domains with opposite electric polarization. The physics of these exotic solitons will serve to describe transient processes in ferroelectric polymers, linking optical- and low-frequency properties. The promising example of such an (AB)x conjugated polymer has already appeared but was not yet tested for ferroelectricity. A wide chemical search is necessary because of a problematic competition of an anti-ferroelectric phase, whose occurrence depends on complicated details of the interchain coupling. more...

International audience; We compare the ferroelectricity for two families of synthetic conductors: the experimentally found ferroelectricity in organic crystal like (TMTTF)2X and a plausilble ferroelectricity in specially designed polyene chains. The difference of the polymer with respect to the organic conductor is the reverse of the build-in (now the sites) and spontaneous (now the bonds) effects of dimerizations. The theory predicts the existence of solitons (dimerization kinks) with non-integer variable charges, both with and without the spin. With today's understanding, we see them as walls separating domains with opposite electric polarization. Their physics will serve to relate transient ferroelectric processes and the visible range optics. more...

We outline a theory of coexisting elastic and plastic deformations in sliding Charge Density Waves. They occur in the course of the conversion from the normal current at the contact to the collective one in the bulk. Several mechanisms of phase slips via creation and proliferation of dislocations are compared. We present a modeling which helps to interpret space-resolved studies in recent [1] and earlier [2] X-ray experiments, in multi-contact [3] and optical [4] studies. more...

A complete picture of phenylene-based polymers is developed which unifies features of band and molecular exciton models. It incorporates major experimental findings in direct and photoinduced optical absorption, in stimulated photoemission and photoconductivity. Our theoretical picture is based upon a band description for electronic states, while invoking corrections from Coulomb interactions. We demonstrate the existence of different types of Coulomb excitons and their roles in optical absorption. We show that a low binding energy-emitting exciton also dominates in the fundamental absorption. Contradictions in the current modeling state-of-the-art are displayed and discussed. For poly(phenylene vinylene) (PPV)-type polymers, we give new assignments for the most disputed features; for oligomers we identify new ones as edge states. In applying our model to the poly(phenylene) (PPP) family, more progress is available due to analytical results covering not only spectra but also the oscillator strength. We conclude similar assignments as for PPV and emphasize the delocalized nature of basic features. An important and intriguing peculiarity of PPP- compared with PPV-based polymers is the possible level inversion between excitons. Comparison is made to available optical and electron energy loss spectroscopy (EELS) data. Our conclusions are suggestive for future light-polarized experiments. more...

Various topics in condensed matter physics are cited as potential beneficiaries of non-destructive 100 T magnets now being designed. These include layered systems, metals, superconductors, semi-metals, narrow gap and doped semiconductors, as well as systems of spin-polarized superstructures, real space Cooper pairs, and bipolarons. An extensive bibliography is provided. more...

We present a consistent theoretical picture for optical properties of phenyl based polymers, especially for the PPV family. The model is based upon an analytical solution for the band structure of PPV oligomers, while invoking the dominant Coulomb corrections for electron-hole interactions. The adjustable parameters are only the common shift for the bands centers of gravity and a dielectric susceptibility at small distances. Our picture gives a clear understanding for the origin of all possible transitions in linear and nonlinear optics. We describe both tightly bound localized excitons and excitons of intermediate range (i.e. of both the Frenkel and Wannier-Mott types). The quantitative description of excitons is obtained from the long range Coulomb interactions, We emphasize where the ring torsion plays a role in the overall energy minimization of the excited state. This article provides theory details for the joint article [S. Brazovskii, N. Kirova, A.R. Bishop, V. Klimov, D. McBranch, N.N. Barashkov, J.P. Ferraris, Opt. Mater. 9 (1998) 472], where a complete picture was outlined. more...

We present a combined experimental and theoretical study of the ground and photoexcited optical properties of a model oligomer of PPV, MEH-DSB. Our theoretical picture is based upon a band description of electronic states of PPV oligomers, while invoking corrections from Coulomb interactions. The necessary discrete energy levels at low and intermediate energies appear naturally, in addition to the lower energy delocalized states. On this basis we identify the most important features in direct optical absorption for both high (4–6 eV) and low (2–4 eV) photon energies as well as in photoinduced absorption (PA) and stimulated photoemissions (SE) in MEH-DSB solutions, which represent the limit of noninteracting oligomers. While in agreement with previous interpretations for three absorption peaks (2.74, 4.46 and 6.2 eV), we give a new assignment for the most disputed 3.62 eV one as well as for the two PA peaks. more...

The bipolarons appear to be the main entity for charge collection in conducting polymers. But their existence is challenged by the Coulomb repulsion. We study the stability of a bipolaron (BP) as a function of the strength of the long range Coulomb interaction U with and without impurities for both weak and strong electron-phonon coupling (α). We find that in a free state the BP is stable only for small values of U for the weak coupling limit but stays stable until relatively large U in the strong coupling case. Being bound to a dopant, the bipolaron becomes stable in a wide range of U. Free BPs near the metal-polymer contact also are stabilized due to a screening by image charges. These results are important for charge injection at polymer-metal interfaces in the context of organic light-emitting diodes. more...

The plasticity of vortex crystals, their melting at the line T m (B) or the corresponding freezing of the vortex liquid are on agenda in current studies of layered superconductors. We review the NMR experiments and present a related theory which prove an unexpectedly large concentration of highly diffusive thermally activated defects: interstitials and vacancies below T m and indicate a presence of unbound 2D dislocations above T m . Also we interpret the critical 2D regime of freezing above T m . The picture is based on the analysis of the longitudinal relaxation rate W(T, B) of the 1 H NMR in the layered organic superconductor κ-BEDT with respect to a developed theory of the NMR relaxation by defects and critical fluctuations. The high magnitude of the peak in W at T m , its sharpening at lower fields B ~ 1 Tsl and especially the ≪master curve ≫ structure in the family of lines W(T, B = const) at the low T slope of the peak lead to above conclusions. more...

We review recent NMR studies of a layered organic superconductor of the (BEDT) 2 X family. First the normal state prop erties are discussed. The central issue is the importance of the interplay between antiferromagnetism and superconductivity in these materials demonstrated by the observation of a pseudogap developing prior to the superconducting transition. The use of high pressure to tune the amplitude of AF fluctuations enables us to draw a general phase diagram of the family. In the second part the NMR experiments in the superconducting state are presented. One of the fundamental questions addressed by these experiments is the symmetry of the order parameter related to the pairing mechanism. The most spectacular NMR measurements are those performed in the lock-in state, which give access to the density of superconducting excitations at low energy. These experiments suggest that the pairing state may be unconventional featuring an anisotropic superconducting gap, possibly with nodes. more...

NMR experiments on Rb 4 C 60 performed under pressure are presented. The temperature dependence of the 13 C NMR relaxation rate T 1 −1 shows two activated behaviors coexisting at ambient pressure; the lowest activation energy disappears under pressure in favor of the emerging Korringa law. The theory is suggested to describe the Rb 4 C 60 as a Jahn-Teller crystal with corresponding consequences for electronic band spectra and for self-trapped states. Experiments are interpreted in terms of two relaxation channels: one due to intramolecular triplet exitons; the other being related to electron-hole excitations through an indirect band gap. more...

We consider electronic properties of interfaces with doped conducting polymers. Two peculiar features are emphasized: the possibility of polaronic and bipolaronic states of electrons (holes) and the mobility of ions within the depletion layer. The mutual diffusion of various types of charges and the transformation of electronic states are considered. On this basis we describe the stationary characteristics and the hysteresis at the Schottky contacts and the effect of photoluminescence quenching and enhancement in a light-emitting device (LED). more...

We suggest a theory for the recently observed frequency dependent low temperature anomaly of the dielectric susceptibility ɛ in Charge and Spin Density Waves, emphasizing interference of collective and local type of pinning. The local pinning is characterized by metastable plastic deformations: neutral bisolitons or pairs of dislocation loops. The weak collective pinning is governed by the elasticity hardening due to Coulomb interaction. more...

Discoveries of the ferroelectric (FE) anomaly (Nad, Monceau, et al.) and the related charge disproportionation (S. Brown et al.) call for a revaluation of the phase diagram of the (TMTTF) 2 X compounds and return the attention to the interplay of electronic and structural properties. We shall describe a concept of the combined Mott–Hubbard state as the source for the ferroelectricity. We shall demonstrate the existence of two types of spinless solitons: the π -solitons, the holons, are observed via the activated conductivity; the noninteger α -solitons are responsible for the depolarization of the FE order. We propose that the (anti) ferroelectricity does exists hiddenly even in Se subfamily, giving rise to the unexplained yet optical peak. We remind then the abandoned theory by the author and Yakovenko for the universal phase diagram which we contrast with the recent one. more...

We derive and study the two-fluid dissipative hydrodynamics equations for the Charge Density Wave (CDW) plastic flow in the presence of a homogeneous distribution of defects: solitons and dislocations. For a one-dimensional development of the injection current impulse we find that the first electric field E∞ ∋ j∞ and the nominal CDW current j∞ are established along the sample length in a very short time. Later on the diffusion front passes along with a constant velocity bE∞, where b is a mobility of solitons. It is followed by growth of the soliton concentration ϱ, and by decrease of local coherent CDW current j ∋ E. At largest time t they develop as j ∋ ϱ −1 s ∋ t −1 3 or as ∋ («/t) 1 3 . The total electric current is nearly additive J ≈ j + 2js being almost constant. Also a stationary distribution is found at the presence of a constant CDW current passing by the injective terminal. It is characterized by a step-like profile of the defects concentration. The pseudostationary time-limited regime is found for the minority carriers injection. more...

The band structure and the electric field distribution at the metal - polymer junction are considered. In contrast to a usual picture of band bending near the contact for common semiconductors the branching of bands takes place and inside the former gap the new allowed energy bands appear. The Fermi-level of the metal always lies inside the energy gap of the polymer independent on the value and sign of the voltage applied across the contact. Single-electron (polarons) majority carriers created by the junction injection or by the interband absorption are affected by an effective force, which pulls them to the contact interface. The single-electron minority carriers in the presence of the superstructure of solitons (bipolarons) do reverse their charge by recombining with two solitons (one bipolaron). The depletion layer forms via conversion of bipolarons to polarons. The possible influence of the band branching on the contact barrier and optical properties are discussed. more...

We consider the structure of a distorted Charge Density Wave /CDW/ near a side contact to a metal. The electric field screening and the charge penetration proceed via inhomogeneous distribution of solitons and/or dislocations. In the presence of these plastic deformations we study selfconsistent equations for elastic and Coulomb fields. For high temperatures we find the soliton density distribution through the sample depth and calculate the capacitance. For low temperatures and concentrations we study the fields and induced surface charges for a single dislocation near the metal surface. At low temperatures and high concentrations a periodic structure of dislocations emerges at some critical voltage between the metal and the CDW. At small charges near threshold voltage the dislocations are far separated and, unexpectedly, deeply located. So the contact region naturally provides both generation and storage of topological defects. With the longitudinal current being applied, these defects will nucleate phase-slip s for the CDW sliding. more...

Electronic properties of quasi onedimensional conductors with charge density waves (CDW) are peculiar for two reasons. First is related to translational degeneracy of CDW ground state which leads to the phenomena of Frohlich conductivity1,2. It shows itself in a giant dielectric susceptibility, in nonlinear and nonstationary effects (see proceedings and the reviews3–7). The second reason is related to a strong interaction of CDW deformations with normal electrons, which leads to their fast selftrapping in the course of conversion to various kinds of solitons8’9. Extensive experimental studies are devoted to the Frolich conductivity (see reviews by Fleming, Gill, Gruner, Jerome, Nad’, Ong, Schlenker et all3–6). At the same time physics of solitons is mainly studied at another substance — polyacetylene10’11, where effects of CDW sliding are absent for the case of two-fold commensurability. more...

The effects of π - electrons for the crystal structure in polyacethylene are discussed. The local crystallografic modifications caused by solitons are considered. The role of twistons in formation of hexagonal phase is discussed. more...

We complete the solid state physics approach to optics of conjugated polymers which allows now to take into account electronic correlations (EC). Our model combines the long range electron-hole (e-h) Coulomb attraction with a specific effect of strong on-site e-h repulsion. The theory operates with a few parameters which can be determined experimentally or from ab initio calculations. The model explains, exploits and organizes various experimental and numerical findings. E.g. we connect such different questions as shallow singlet (S) and deep triplet (T) excitons in phenylenes, A g -B u crossing in polyenes, common I/L energy dependencies in oligomers, etc. more...

We present an x-ray diffraction study of 2.8 at.% V-doped blue bronzes. At low temperature, we have observed both an intensity asymmetry of the ±2k F satellite reflections relative to the pure compound, and a profile asymmetry of each satellite reflections. The profile asymmetry is due to Friedel oscillation around the V substituant and the intensity asymmetry is related to the charge density wave (CDW) pinning. These two effects give access to the local properties of CDW in disordered systems, including the pinning and even the phase shift of Friedel oscillations. more...

For phenyl based polymers we describe the absorption underlying effects of the long range Coulomb interactions -for both bound and free e - h states at weak and moderately strong electric fields when higher excited states are destroyed while the primary one is preserved for which we have found the ionization probability. The theory is based on analyzing the series of excitons as weakly bound states of delocalized electron and a hole. more...

The rich order parameter of Spin Density Waves allows for an unusual object of a complex topological nature: “Chimeras” composed by a half — integer dislocation combined with a semi — vortex of the staggered magnetization. They become energetically favorable due to enhanced Coulomb interactions. Their generation changes the NBN frequency. more...

We study the stability of a bipolaron as a function of the strength of the Coulomb interaction in conjugated polymers. While strong Coulomb interactions will destabilize the bipolaron, we find impurities and image forces tend to stabilize it, which implies that bipolarons may be important for charge injection at polymer-metal interfaces in the organic LEDs. more...

The recently successful model [1, 2] for optical properties of PPV based polymers is applied to the PPP family. More progress is available thanks to analytical results covering not only spectra but also the oscillator strength. We conclude similar assignments and emphasize the delocalized nature of basic features. We demonstrate the existence of different types of Coulomb excitons and their roles in the optical absorption. An important and intriguing difference compared with PPV based polymers is the level inversion for the more strongly localized interband exciton. Comparison is made to available optical and EELS data [3, 4, 5]. Our conclusions are suggestive for the future light — polarized experiments. more...

We consider bound states of bipolarons with monovalent dopants, their transformation under illumination and by charge injection. These complexes provide effective traps for the minority carriers. On this basis we describe the photoluminescence quenching in LED, the stationary characteristics and hysteresis at the Schottky contacts. more...

We have considered a quasiclassical quantization of solitons (kinks, polarons, bipolarons) for the Peierls model with both a degenerate and a nondegenerate ground state. We have calculated the electric current and the charge of quantum excitations, which, as is proved, is distinct from the local charge of classical excitations. more...

There is a number of materials where bipolarons (BP) are probably the main extrinsic carriers. We discuss a dense system of BP produced by the equilibrium charge injection at the surface of Schottki or MIS junctions. Possible super-conductivity of this system due to the Bose-condensation of BP is studied. more...

The frequency dependent conductivity σ(ω) completely taking into account the interaction between electrons is studied. The shape and the temperature dependence of optical absorption near the frequency of a molecular phonon activated due to the interaction with electrons are found. For a system with attractive sign of the e - e backward scattering amplitude g 1 e - e interactions and are critical to the sign of g 1 . more...

It is possible to induce excess charge on the surface of dielectric La 2 CuO 4 by the field effect of a transistor or in the Schottky junction. Superconductivity can be observed in this two-dimensional system. more...

Soliton states in SDW systems are investigated. The form, the charge, and the spin of the soliton in linearly polarized SDW systems are found. Admissible types of solitons in helically polarized SDW systems are described. more...

Exactly soluble models for electrons on a deformable discrete chain are found. They include typical continuous Peierls models as special limits. The chain structure, electronic spectrum and thermodynamic functions in the ground state are found. The region of a nearly half filled band corresponding to the polyacetylene model is described in detail. more...