Finland Love Song

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Screening effects in the electron-optical phonon interaction

We show that recently reported unusual hardening of optical phonons renormalized by the electron-phonon interaction is due to the neglect of screening effects. When the electron-ion interaction is properly screened optical phonons soften in three dimension. It is important that for short-wavelength optical phonons screening is static while for long-wavelength optical phonons screening is dynamic. In two-dimensional and one-dimensional cases due to crossing of the nonperturbed optical mode with gapless plasmons the spectrum of renormalized optical phonon-plasmon mode shows split momentum dependence.Comment: 7 page

Effect of electron-phonon interaction on the shift and attenuation of optical phonons

Using the Boltzmann equation for electrons in metals, we show that the optical phonons soften and have a dispersion due to screening in agreement with the results reported recently [M. Reizer, Phys. Rev. B {\bf 61}, 40 (2000)]. Additional phonon damping and frequency shift arise when the electron--phonon interaction is properly included.Comment: 4 pages, late

Avelumab in European patients (pts) with metastatic Merkel cell carcinoma (mMCC): Experience from an ad-hoc expanded access program (EAP)

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Polaron band formation in the Holstein model

We present numerical exact results for the polaronic band structure of the Holstein molecular crystal model in one and two dimensions. The use of direct Lanczos diagonalization technique, preserving the full dynamics and quantum nature of phonons, allows us to analyze in detail the renormalization of both quasiparticle bandwidth and dispersion by the electron-phonon interaction. For the two-dimensional case some of our exact data are compared with the results obtained in the framework of a recently developed finite cluster strong-coupling perturbation theory.Comment: 10 pages (LaTeX), 6 figures (ps), submitted to Phys. Rev.

Electron-phonon renormalization in small Fermi energy systems

The puzzling features of recent photoemission data in cuprates have been object of several analysis in order to identity the nature of the underlying electron-boson interaction. In this paper we point out that many basilar assumptions of the conventional analysis as expected to fail in small Fermi energy systems when, as the cuprates, the Fermi energy $E_{\rm F}$ is comparable with the boson energy scale. We discuss in details the novel features appearing in the self-energy of small Fermi energy systems and the possible implications on the ARPES data in cuprates.Comment: 4 pages, 5 eps figures include

Nonanalytic corrections to the specific heat of a three-dimensional Fermi liquid

We revisit the issue of the leading nonanalytic corrections to the temperature dependence of the specific heat coefficient, $\gamma (T)=C(T)/T,$ for a system of interacting fermions in three dimensions. We show that the leading temperature dependence of the specific heat coefficient $\gamma (T)-\gamma (0) \propto T^3 \ln T$ comes from two physically distinct processes. The first process involves a thermal excitation of a single particle-hole pair, whose components interact via a nonanalytic dynamic vertex. The second process involves an excitation of three particle-hole pairs which interact via the analytic static fixed-point vertex. We show that the single-pair contribution is expressed via the backscattering amplitude of quasiparticles at the Fermi surface. The three-pair contribution does not have a simple expression in terms of scattering in particular directions. We clarify the relation between these results and previous literature on both 3D and 2D systems, and discuss the relation between the nonanalyticities in $\gamma$ and those in spin susceptibilities

Optical conductivity in the normal state fullerene superconductors

We calculate the optical conductivity, $\sigma(\omega)$, in the normal state fullerene superconductors by self-consistently including the impurity scatterings, the electron-phonon and electron-electron Coulomb interactions. The finite bandwidth of the fullerenes is explicitely considered, and the vertex corection is included $a$ $la$ Nambu in calculating the renormalized Green's function. $\sigma(\omega)$ is obtained by calculating the current-current correlation function with the renormalized Green's function in the Matsubara frequency and then performing analytic continuation to the real frequency at finite temperature. The Drude weight in $\sigma(\omega)$ is strongly suppressed due to the interactions and transfered to the mid-infrared region around and above 0.06 eV which is somewhat less pronounced and much broader compared with the expermental observation by DeGiorgi $et$ $al$.Comment: 6 pages, 4 figures. To be published in Physical Review B, July 1

Temperature dependence of the collective mode and its influence on the band splitting in bilayer cuprates

The recently observed bilayer splitting in high-T$_c$ cuprates is analyzed within a model where the charge carriers are coupled to a phenomenological bosonic spectrum which interpolates between the marginal Fermi liquid structure and collective mode type behavior as a function of temperature. We argue that the origin of the collective mode is probably associated with dynamic incommensurate charge density waves. Moreover it is shown that the resulting temperature dependence of the self-energy $\Sigma$ is in good agreement with $\Sigma$ as extracted from angle-resolved photoemission data.Comment: 6 pages, 4 figures, accepted for PR

Collective Modes and the Superconducting State Spectral Function of Bi2212

Photoemission spectra of the high temperature superconductor Bi2212 near (pi,0) show a dramatic change when cooling below Tc: the broad peak in the normal state turns into a sharp low energy peak followed by a higher binding energy hump. Recent experiments find that this low energy peak persists over a significant range in momentum space. We show in this paper that these data are well described by a simple model of electrons interacting with a collective mode which appears only below Tc.Comment: 4 pages, revtex, 4 encapsulated postscript figure