Exact solution of electronic transport in semiconductors dominated by scattering on polaronic impurities

The scattering of electrons on impurities with internal degrees of freedom is bound to produce the signatures of the scatterer's own dynamics and results in nontrivial electronic transport properties. Previous studies of polaronic impurities in low-dimensional structures, like molecular junctions and one-dimensional nanowire models, have shown that perturbative treatments cannot account for a complex energy dependence of the scattering cross section in such systems. Here we derive the exact solution of polaronic impurities shaping the electronic transport in bulk (3D) systems. In the model with a short-ranged electron-phonon interaction, we solve for and sum over all elastic and inelastic partial cross sections, abundant in resonant features. The temperature dependence of the charge mobility shows the power-law dependence, $\mu(T)\propto T^{-\nu}$, with $\nu$ being highly sensitive to impurity parameters. The latter may explain nonuniversal power-law exponents observed experimentally, e.g. in high-quality organic molecular semiconductors.Comment: 5 pages, 6 figure

Competing Ground States of the New Class of Halogen-Bridged Metal Complexes

Based on a symmetry argument, we study the ground-state properties of halogen-bridged binuclear metal chain complexes. We systematically derive commensurate density-wave solutions from a relevant two-band Peierls-Hubbard model and numerically draw the the ground-state phase diagram as a function of electron-electron correlations, electron-phonon interactions, and doping concentration within the Hartree-Fock approximation. The competition between two types of charge-density-wave states, which has recently been reported experimentally, is indeed demonstrated.Comment: 4 pages, 5 figures embedded, to appear in J. Phys. Soc. Jp

Topological Dislocations and Mixed State of Charge Density Waves

We discuss the possibility of the ``mixed state'' in incommensurate charge density waves with three-dimensional order. It is shown that the mixed state can be created by applying an electric field perpendicular to the chains. This state consists of topological dislocations induced by the external field and is therefore similar to the mixed states of superfluids (type-II superconductor or liquid Helium II). However, the peculiar coupling of charge density waves with the electric field strongly modifies the nature of the mixed state compared to the conventional superfluids. The field and temperature dependence of the properties of the mixed state are studied, and some experimental aspects are discussed.Comment: 10 pages, Revtex format, no figures, to appear in Phys. Rev. Let

Complex paths for regular-to-chaotic tunneling rates

In generic Hamiltonian systems tori of regular motion are dynamically separated from regions of chaotic motion in phase space. Quantum mechanically these phase-space regions are coupled by dynamical tunneling. We introduce a semiclassical approach based on complex paths for the prediction of dynamical tunneling rates from regular tori to the chaotic region. This approach is demonstrated for the standard map giving excellent agreement with numerically determined tunneling rates.Comment: 5 pages, 4 figure

The Holstein Polaron

We describe a variational method to solve the Holstein model for an electron coupled to dynamical, quantum phonons on an infinite lattice. The variational space can be systematically expanded to achieve high accuracy with modest computational resources (12-digit accuracy for the 1d polaron energy at intermediate coupling). We compute ground and low-lying excited state properties of the model at continuous values of the wavevector $k$ in essentially all parameter regimes. Our results for the polaron energy band, effective mass and correlation functions compare favorably with those of other numerical techniques including DMRG, Global Local and exact diagonalization. We find a phase transition for the first excited state between a bound and unbound system of a polaron and an additional phonon excitation. The phase transition is also treated in strong coupling perturbation theory.Comment: 24 pages, 11 figures submitted to PR

Characterization of halogen-bridged binuclear metal complexes as hybridized two-band materials

We study the electronic structure of halogen-bridged binuclear metal (MMX) complexes with a two-band Peierls-Hubbard model. Based on a symmetry argument, various density-wave states are derived and characterized. The ground-state phase diagram is drawn within the Hartree-Fock approximation, while the thermal behavior is investigated using a quantum Monte Carlo method. All the calculations conclude that a typical MMX compound Pt_2(CH_3CS_2)_4I should indeed be regarded as a d-p-hybridized two-band material, where the oxidation of the halogen ions must be observed even in the ground state, whereas another MMX family (NH_4)_4[Pt_2(P_2O_5H_2)_4X] may be treated as single-band materials.Comment: 16 pages, 11 figures embedded, to be published in Phys. Rev.

CDW screening of the charged impurity

A mechanism of screening of the charged impurity by the CDW is described. The carriers released by the impurity are absorbed by the CDW lattice and situated around the impurity. This results in the creation of the dislocation loop in this lattice. The chains with additional charges carry the 2 π solitons, which provide for the localized electronic states. The described screening picture is derived using the continuous approximation in the treatment of the deformations of the CDW lattice.Nous décrivons le mécanisme d'écrantage d'une impureté chargée par l'onde de densité de charge (ODC). Les porteurs de charge se détachent de l'impureté, entrent dans le réseau de l'ODC et se situent au voisinage de l'impureté. Ceci résulte en la création d'une boucle de dislocations dans le réseau de l'ODC. Les chaînes avec les charges supplémentaires portent les solitons 2 π, associés aux états électroniques localisés. Cette description d'écrantage est obtenue à partir de l'approximation continue pour les déformations du réseau de l'ODC

Soliton lattice melting-functional integral method

Structure factors which describe the melting of the soliton lattice at low temperatures are found for the epitaxial and the CDW one-dimensional commensurability problem. The relation to the infra-red problem in the sine-Gordon approach is briefly discussed.Nous déterminons les facteurs de structure pour la fonte à basse température du réseau de soliton présent dans le problème de la commensurabilité à une dimension, dans le cas d'épitaxie et d'ondes de densité de charge. Nous discutons brièvement de la relation de ce problème avec celui de l'infra-rouge dans l'approche sine-Gordon

Electron mechanism for the tilting transition in La2-x SrxCuO4

It is shown that the tilting deformation is couplet to the electrons through the tilting induced variation of the Umklapp matrix elements. The latter are important only for small concentrations of Sr if the electron-electron interaction, (which are assumed to be repulsive), are reasonably small. The leading term in the resulting deformation energy is quadratic in the tilting deformation and leads to the critical devease of the tilting mode frequency when the temperature is lowered. The resistivity, although enhanced by Umklapps, is continuous through the tilting transition. The model bears some ressemblence to that developed previously for 4k F deformations in organic superconductors. Some consequences of the model for the high Tc superconductivity are briefly discussed.Nous montrons que la déformation qui fait onduler les plans CuO2 est couplée aux électrons par l'intermédiaire de la variation des éléments de matrice Umklapp dans l'interaction électron-électron. Ces derniers ne sont importants que pour de faibles concentrations de Sr, si les interactions, supposées alors répulsives, sont suffisamments petites. Le premier terme dans la contribution à l'énergie de déformation est quadratique en déformation et diminue de façon critique la fréquence des modes d'ondulation lorque la température décroît. La résistivité, bien qu'augmentée par Umklapp, est continue à travers la transition à la phase ondulée. Notre modèle ressemble quelque peu à celui développé précédemment pour les supraconducteurs organiques. Nous discutons aussi brièvement les propriétés du modèle qui concernent la supraconductivité à Tc élevée

Generation of the coherent pulses by the CDW-motion. Solutions of the microscopic model equations

The collective transport of charge density waves (CDW) converts into an ordinary current at the contacts with a normal metal. In the present work this conversion is proposed to proceed via the process of phase slippage (PS). The CDW in the quasi-one-dimensional system with a nested Fermi surface and impurities is described by the nonlinear differential equation derived earlier. This equation is solved numerically for semi-infinite samples, as well as for finite samples with both edges fixed. The analysis of solutions is carried out for electrical fields E and sample lengths L which are respectively one to two orders of magnitude larger and smaller than the actual experimental values. This leads to the following results : the PS solutions are one-periodic functions of time, with the distance of the PS centre from the fixed end behaving like E- 0.284 in the limit of small E. The coherent CDW transport in the finite samples occurs above the threshold field which varies as L-1.23. The pulses in the voltage generated by PS processes are also analysed. The results are in a good agreement with the experimental data for the length dependence of the threshold field and with some properties of the periodic noise in e.g. NbSe3 and TaS3.Le transport collectif par les ondes de densité de charge (CDW) se transforme en un courant ordinaire dans les contacts avec le métal normal. Dans notre étude ce processus se produit par le glissement de phase (PS) de CDW. Le CDW dans un système quasi unidimensionnel avec une surface de Fermi à « nesting » et en présence d'impuretés est décrit par une équation différentielle non linéaire obtenue auparavant. Nous résolvons cette équation numériquement pour des échantillons semi-infinis et finis. L'analyse des solutions est faite pour des champs électriques E et les longueurs d'échantillon L qui sont respectivement d'un à deux ordres de grandeur plus grands et petits que les valeurs expérimentales actuelles. Il s'ensuit que les solutions PS sont fonctions du temps à une période, avec la distance du centre PS au contact variant comme E-0,284 dans la limite des petits champs. Le transport cohérent par CDW existe au-dessus d'un champ de seuil qui varie comme L-1,23. Nous avons examiné aussi les pulses dans le voltage, produits par le processus de PS. Les résultats sont en bon accord avec la dépendance en longueur des champs de seuil et certaines propriétés de bruit périodique, observés dans NbSe3 et TaS3