Ionic plasma screening and long-range electron correlations in quasi-one-dimensional conductors

In quasi-one-dimensional systems with the intercalation-type doping, the dynamical response of dopant ions can substantially affect the interplay of density-wave and superconducting instabilities. A generic model system of Coulombically coupled Luttinger-liquid chains augmented by the interaction with the ion displacements is exactly solved in the forward-scattering channel providing for the resulting system excitations and electron correlations. For a jellium-like ion response, the effect of the bare electron–electron repulsion is essentially canceled by the ions. Superconducting correlations can then be developed due to a non-polarizational interaction with an additional phonon mode.     

Four-terminal resistance in a clean interacting quantum wire with invasive contacts

We investigate the behavior of the four-terminal resistance R_4pt$R_{4\mathit{pt}}$ in an interacting quantum wire described by a Luttinger liquid with an applied bias voltage V and coupled to two voltage probes. We extend previous results, obtained for very weakly coupled contacts, to the case in which the effects of the probes become non-trivially correlated.     

Photon-assisted shot noise through a quantum dot coupled to Luttinger liquid

Photon-assisted shot noise through a quantum dot coupled to Luttinger liquid leads is considered using nonequilibrium-Green-function-method. We find that the effect of ac field on the differential shot noise is different for different intralead electron interaction. The inelastic channels associated with photon-assisted-tunneling can dominate electron transport for some ac parameters.     

Organic conductors and superconductors: A comparative survey

The nature of the electronic and structural ground states observed in the two-stack TCNQ charge transfer salts, the [TMTS(T)F]₂X and (BEDT-TTF)₂X single-stack series successively synthesized during the last 15 years, is reviewed. Special attention is devoted to physical parameters, such as dimensionality of the electron gas, electron-electron interactions and coupling between electronic and structural degrees of freedom, which seem to control the physics of these organic conductors.     

Spinful fermionic ladders at incommensurate filling: Phase diagram,local perturbations,and ionic potentials

We study the effect of external potential on transport properties of the fermionic two-leg ladder model. The response of the system to a local perturbation is strongly dependent on the ground state properties of the system and especially on the dominant correlations. We categorize all phases and transitions in the model (for incommensurate filling) and introduce “hopping-driven transitions” that the system undergoes as the inter-chain hopping is increased from zero. We also describe the response of the system to an ionic potential. The physics of this effect is similar to that of the single impurity, except that the ionic potential can affect the bulk properties of the system and in particular induce true long range order.     

Polarized infrared reflectivity study in charge density wave conductor Tl0.3MoO3

Polarized infrared reflectivity measurements between 300 and 10 K have been carried out on charge density waves (CDW) conductor blue bronze Tl_0.3MoO₃. Three important features are observed: (i) A bump at 1155 cm⁻¹ in the reflectivity spectra of Tl_0.3MoO₃ at 300 K is a precursor of the Peierls gap due to optical excitations across a pseudogap, and this kind of Peierls-like gap opens gradually with decreasing temperature from 180 to 160 K. (ii) The three sharp modes as “triplet” of infrared reflectivity between 800 and 1000 cm⁻¹ of Tl_0.3MoO₃ along [1 0 2] axis show red shift compared to K_0.3MoO₃ and Rb_0.3MoO₃, which is assigned to the increase of the distance of Mo-O bond with the substitution of thallium ions. (iii) Two peaks at about 514 and 644 cm⁻¹ in the far-infrared reflectivity spectra of Tl_0.3MoO₃ along [1 0 2] direction are suggested to be the electronic transitions from the valence band to the midgap state and from occupied midgap state to the conduction band, respectively.     

Non-equilibrium and band tailing in organic conductors

The concept of band tailing with focal point and width of the tail from IR absorption spectra of different organic conductors is found valid even for thermal and elastic changes. The experimental situations like change of solvents, method of preparation, applied pressure and pressure cycle apart from compositions is analyzed within the framework of tailing of states. Non-equilibrium due to coupling between applied energy and free electrons can be responsible for the exponential relaxation from non-equilibrium to equilibrium     

Coupling between molecular chains and anions in (TMTTF)2X salts

Upon cooling the (TMTTF)₂X salts undergo transitions to various ordered states in the charge and spin degrees of freedom; these different ground states depend on the anions X. It turns out that the anions are not simple spacers between the TMTTF stacks, but their symmetry and size play an important role as well as the dipole moment and polarizability. Here we discuss the coupling between TMTTF-molecules and anions with different symmetries.     

Directed transport in quantum Hall bilayers

The pseudo-spin model for a double layer quantum Hall system with the total landau level filling factor ν=1 is discussed. In contrast to the “traditional” model where the interlayer voltage enters as a static magnetic field along pseudo-spin hard axis, taking into account the realistic experimental situation, in our model we interpret the influence of applied voltage as a source of additional relaxation process in the double layer system. We show that the Landau-Lifshitz equation for the considered pseudo-magnetic system well describes existing experimental data and reduces to the dc driven and damped sine-Gordon equation. As a result, the mentioned model predicts novel directed intra-layer transport phenomenon in the system. In particular, unidirectional intra-layer energy transport can be realized due to the motion of topological kinks induced by applied voltage. Experimentally this should be manifested as counter-propagating intra-layer inhomogeneous charge currents proportional to the interlayer voltage and total topological charge of the pseudo-spin system.     

Charge transport mechanism in pressed pellets of polymer proton conductors

The charge transport inside some polymer proton conductors, prepared by chemical doping of poly(propargyl alcohol) and poly(p-diethynylbenzene) with acids, or by electrochemical polymerisation of thionaphtheneindole, has been investigated. All the systems, studied as powder pressed pellets between two gold electrodes, show very low electrical conductivity due to electrons motion. In presence of environmental humidity the conductivity increases dramatically as a consequence of proton migration through the material. A mechanism for the charge transport through the materials, based on the proton conductivity of a thin layer of acid aqueous solution adherent to the polymer grains, has been hypothesised. Since the investigated doped polymers show a reversible conductivity variation as a function of water content, they are proposed as materials for humidity sensor construction.     

Simulation of prefactor anomalies in superionic conductors in the case of arbitrary energy losses

Based on a sticking-probability formulation, we have considered a breakdown of absolute rate theory in relation to prefactor anomalies in superionic conductors in the case of arbitrary energy losses of ions. We present simulation results concerning the prefactor dependence on the magnitude of the average energy loss in the energy-transfer range from 10⁻³ to 0.46 kT and the energy dependence of the sticking probability for ions.     

Nucleus-acoustic solitary waves in white dwarfs

The formation of nucleus-acoustic solitary waves (NASWs), and their basic properties in white dwarfs containing non-relativistically or ultra-relativistically degenerate electrons, non-relativistically degenerate light nuclei, and stationary heavy nuclei have been theoretically investigated. The reductive perturbation method, which is valid for small but finite amplitude NASWs, is used. The NASWs are, in fact, associated with the nucleus acoustic (NA) waves in which the inertia is provided by the light nuclei, and restoring force is provided by the degenerate pressure of electrons. On the other hand, stationary heavy nuclei maintain the background charge neutrality condition. It has been found that the presence of the heavy nuclei significantly modify the basic features (polarity, amplitude, width, and speed) of the NASWs. The basic properties are also found to be significantly modified by the effects of ultra-relativistically degenerate electrons and relative number densities of light and heavy nuclei. The implications of our results in white dwarfs are pinpointed.     

Combined breathing-kink modes in the FPU lattice

Combined breather-kink modes have been observed in several systems. Here we show that in the FPU lattice, small amplitude breathing-kink modes are three-soliton solutions of an associated mKdV equation. Since this is integrable, the modes can be constructed using the Bäcklund transform. As well as finding explicit solutions, we consider the stability of the combined mode using variational techniques and illustrate stability for some parameter values and instability for others.     

Bond and charge ordering in low-dimensional organic conductors

We review 35 years of structural studies of quasi-1D organic conductors during which the concepts of 2k_F and 4k_F BOW and CDW have been elaborated. In strongly correlated quarter filled band systems these instabilities give rise to SP, DM and CO ground states. We relate these structural features to the instabilities of the 1D electron gas. To stabilize the different ground states the nature of the electron-phonon coupling has to be considered together with the coupling of the organic stacks with the anion sublattice. New results concerning the classification of the SP phase in connection with the adiabatic or antiadiabatic phonon field and its competition with the CO are also introduced.     

Phonon-assisted zero bias anomaly in a single-molecule quantum dot coupled to the Luttinger liquid leads

The joint effects of the electron–phonon interaction and electron–electron interaction in the Luttinger liquid leads on nonequilibrium transport through a single-molecule transistor in the Kondo regime are investigated by using the improved canonical transformation scheme and equation of motion approach. For weak intralead electron interaction, a pronounced dip around zero bias, accompanied by a series of discrete single-electron tunneling peaks is observed in the differential conductance. With the increase of the intralead interaction, the phonon-assisted peaks turn into dips, which demonstrates a phonon-assisted two-channel Kondo physics. For a certain region of interaction strength the inelastic electron tunneling can dominate electron transport. Our results well explain the experiments of zero bias anomaly.     

Closed-form solution for a pair of touching cylindrical conductors in an external electric field

We give expressions for the electric potential and field around two conducting cylinders in contact, in closed form and in terms of elementary functions. The polarizability tensor, and hence the torque acting on the cylinder pair, follow from these results. The surface charge density, and the total charge per unit length on each cylinder, can also be evaluated in closed form. The equal and opposite forces on the two cylinders are found in the case of equal cylinder radii.     

Charge localization in organic conductors (TM)X: The influence of anion ordering

An investigation of the different contributions leading to charge localization in a 1/2 or 1/4 filled band 1D conductor has been conducted through a study of transport properties in the solid solution [(TMTSF)_1-x (TMTTF) _x]₂ReO₄. The existence of an ordering transition of the anions allows to identify two contributions to the electronic potential with wave vector 4k_F. A dominant on-site 4k_F potential besides the bond contribution is revealed when Umklapp scattering is pertinent via the weakening of the localization arising at the (0, 1/2, 1/2) anion ordering which is stabilized under pressure in the compound [(TMTSF) _0.5 (TMTTF)_0.5]₂ReO₄ at variance with the enhancement of localization observed in the homomolecular (TMTTF)₂ReO ₄ material. Received: 13 May 1998 / Revised: 8 July 1998 / Accepted: 9 July 1998     

Fano line shape and anti-crossing of Raman active E2g peaks in the charge density wave state of NbSe2

Low energy Raman scattering from the ab-plane of the 2H polytype single crystal NbSe₂ has been investigated in the normal (N), incommensurate charge density wave (ICDW) and superconducting (SC) phases. The temperature dependence of the polarization resolved Raman response has been obtained for the excitation wavelength of 647 nm and fitted to phenomenological models for the E_2g and A_1g symmetry channels. The A_1g response can be fitted by a simple damped oscillator peak superimposed on continuous background. The E_2g response displays an anti-resonance interference pattern between the inter-layer phonon and the CDW-induced mode such that a hybridized configuration (Fano line shape [1]) is required for modelling. The polarization specific peak maxima positions and line widths as a function of temperature, deduced in this manner, are presented. Partial suppression of the electronic continuum scattering in the Raman shift range up to 110 cm⁻¹ in the A_1g symmetry channel and beyond 300 cm⁻¹ in the E_2g symmetry channel is indicative of high energy electronic states far away from the Fermi surface participating in the ICDW formation.