Fr\"ohlich Polarons from 0D to 3D: Concepts and Recent Developments

I analyse our present understanding of the Froehlich polaron with emphasis on the response properties, in particular optical absorption.Comment: 28 pages, 17 figures, invited lecture at the ESF Exploratory Workshop EW05-105 "Mott's Physics in Nanowires and Quantum Dots", University of Cambridge, United Kingdom, 31 July - 2 August 200

Sum Rule for the Optical Absorption of an Interacting Many-Polaron Gas

A sum rule for the first frequency moment of the optical absorption of a many-polaron system is derived, taking into account many-body effects in the system of constituent charge carriers of the many-polaron system. In our expression for the sum rule, the electron-phonon coupling and the many-body effects in the electron (or hole) system formally decouple, so that the many-body effects can be treated to the desired level of approximation by the choice of the dynamical structure factor of the electron (hole) gas. We calculate correction factors to take into account both low and high experimental cutoff frequencies.Comment: 16 pages, 3 figures, revised version; new results adde

Optical conductivity of a strong-coupling polaron

The polaron optical conductivity is derived within the strong-coupling expansion, which is asymptotically exact in the strong-coupling limit. The polaron optical conductivity band is provided by the multiphonon optical transitions. The polaron optical conductivity spectra calculated within our analytic strong-coupling approach and the numerically accurate Diagrammatic Quantum Monte Carlo (DQMC) data are in a good agreement with each other at large $\alpha \gtrapprox 9$.Comment: 27 pages, 3 figures. Submitted to Physical Review B on June 12, 2013. A revised paper is in preparation. arXiv admin note: substantial text overlap with arXiv:1012.457

Feynman's path-integral polaron treatment approached using time-ordered operator calculus

The Feynman all-coupling variational approach for the polaron is re-formulated and extended using the Hamiltonian formalism with time-ordered operator calculus. Special attention is devoted to the excited polaron states. The energy levels and the inverse lifetimes of the excited polaron states are, for the first time, explicitly derived within this all-coupling approach. Remarkable agreement of the obtained transition energies with the peak positions of the polaron optical conductivity calculated using diagrammatic quantum Monte Carlo is obtained.Comment: 6 pages, 2 figures, to appear in Solid State Communications, presented at the 10th International Conference "Path Integrals - 2010", July 11 - 16, 2010, Washington DC, US

The role of bacterial secretion systems in the virulence of Gram-negative airway pathogens associated with cystic fibrosis

Cystic fibrosis (CF) is the most common lethal inherited disorder in Caucasians. It is caused by mutation of the CF transmembrane conductance regulator (CFTR) gene. A defect in the CFTR ion channel causes a dramatic change in the composition of the airway surface fluid, leading to a highly viscous mucus layer. In healthy individuals, the majority of bacteria trapped in the mucus layer are removed and destroyed by mucociliary clearance. However, in the lungs of patients with CF, the mucociliary clearance is impaired due to dehydration of the airway surface fluid. As a consequence, patients with CF are highly susceptible to chronic or intermittent pulmonary infections, often causing extensive lung inflammation and damage, accompanied by a decreased life expectancy. This mini review will focus on the different secretion mechanisms used by the major bacterial CF pathogens to release virulence factors, their role in resistance and discusses the potential for therapeutically targeting secretion systems

Ground state and optical conductivity of interacting polarons in a quantum dot

The ground-state energy, the addition energies and the optical absorption spectra are derived for interacting polarons in parabolic quantum dots in three and two dimensions. A path integral formalism for identical particles is used in order to take into account the fermion statistics. The approach is applied to both closed-shell and open-shell systems of interacting polarons. Using a generalization of the Jensen-Feynman variational principle, the ground-state energy of a confined N-polaron system is analyzed as a function of N and of the electron-phonon coupling constant. As distinct from the few-electron systems without the electron-phonon interaction, three types of spin polarization are possible for the ground state of the few-polaron systems: (i) a spin-polarized state, (ii) a state where the spin is determined by Hund's rule, (iii) a state with the minimal possible spin. A transition from a state fulfilling Hund's rule, to a spin-polarized state occurs when decreasing the electron density. In the strong-coupling limit, the system of interacting polarons turns into a state with the minimal possible spin. These transitions should be experimentally observable in the optical absorption spectra of quantum dots.Comment: 33 pages, 9 figures, E-mail addresses: [email protected], [email protected], [email protected], [email protected], accepted for Phys. Rev.

Note on the Path-Integral Variational Approach in the Many-Body Theory

I discuss how a variatonal approach can be extended to systems of identical particles (in particular fermions) within the path-integral treatment. The applicability of the many-body variational principle for path integrals is illustrated for different model systems, and is shown to crucially depend on whether or not a model system possesses the proper symmetry with respect to permutations of identical particles.Comment: 15 pages, 1 figure, E-mail address: [email protected]