Local Approximation Of The Holstein Polaron Problem

We review the Dynamical Mean Field Theory of the Holstein Polaron Problem in order to compute the small polaron Green's functions. The Renormalized Perturbation Expansion (RPE) play a central role and allows to compute all the local and non local Green's functions for the electron and the small polaron, for finite or infinite size systems, with periodic or non periodic boundary conditions. We introduce a restricted basis for the phonons to study the decoupling scheme of the Green's functions in a Local Approximation via exact diagonalizations. As a bonus, we furnish all the C/C++ programs built step by step, from a pedagogical point of view.

We show how to set up a Cellular Dynamical Mean Field Theory for the Holstein's polaron problem using the exact solution of a cluster of n sites embedded in a Weiss's field. We show that a restricted basis, that allows excitations of phonons only for n sites at a time, reproduces exactly the equations of the n-site Dynamical Mean Field Theory, and enables to check the proposed decoupling scheme of the Green's functions via Exact Numerical Diagonalizations. We introduce a real space formulation of the Cellular Dynamical Mean Field Theory that applies to any lattice with or without periodic boundary conditions and that allows to partition the lattice into different kinds of clusters.

This book first introduces a single polaron and describes recent achievements in analytical and numerical studies of polaron properties in different e-ph models. It then describes multi-polaron physics as well as many key physical properties of high-temperature superconductors, colossal magnetoresistance oxides, conducting polymers and molecular nanowires, which were understood with polarons and bipolarons.

Problems of Linear Electron (Polaron) Transport Theory in Semiconductors summarizes and discusses the development of areas in electron transport theory in semiconductors, with emphasis on the fundamental aspects of the theory and the essential physical nature of the transport processes. The book is organized into three parts. Part I focuses on some general topics in the theory of transport phenomena: the general dynamical theory of linear transport in dissipative systems (Kubo formulae) and the phenomenological theory. Part II deals with the theory of polaron transport in a crystalline semiconductor. The last part contains a critical account of electron transport in disordered systems, including amorphous substances, with allowance for polaron effects.

High temperature superconducting theory drew controversy after the discovery of superconductors at close to room temperatures. However, a consistent microscopic theory of HT superconductivity based on bipolaron mechanism leads to a better understanding of microscopic and macroscopic description. By presenting aspects of superconductivity now joined in a strict theory rather than separate models this work is especially useful for graduate students.

An enormous theoretical effort has been made to treat electron-phonon coupled systems, with particular emphasis on Many Body aspects for dense electron systems, taking into account continuum as well as lattice polaron effects. Treating such aspects of polaron theory has been made possible because of powerful Many Body techniques which include: Exact Diagonalization techniques, Quantum Monte Carlo approaches, Density Matrix renormalization group and Dynamical Mean Field Theory. All these advances in polaron theory needed to be accompanied by: (i) an equally important advance in material research which produced many new materials such as the high Tc cuprates, the manganites and nickelates and the fullerines; (ii) as well as significant advances in the refinement of experimental analysis and, in particular, the spectroscopic means such as Angel Resolved Photoemission Spectroscopy, X Ray Absorption Spectroscopy (EXAFS, XANES), Pulsed Neutron Diffraction measurements allowing to study the local dynamical lattice de-formations and optical spectroscopy including time resolved measurements. The scope and purpose of this publication is to review both these theoretical and experimental advances which occurred over the last few decades and to introduce the study of such systems, where both strong electron-electron correlations and large electron-phonon coupling strengths play important roles.

The properties of self-localized carriers on a lattice are described at a fairly basic level with an emphasis on modern developments in the theory of strong-coupling superconductivity. Large and small polarons and bipolarons provide a number of new physical phenomena both in the normal and superconducting states. The physics of high temperature superconductors is described and explained.