Ellipsometry study of the c-axis pseudogap in high temperature superconductors with Zn and Ni impurities

Abstract

This thesis reports on infrared ellipsometric studies of the dielectric properties of cuprate high temperature superconductors. Ellipsometry is an advanced spectroscopy technique that allows one to measure directly and with high precision the complex dielectric function of a given material by analyzing the change of the polarization state of light upon reflection on the sample. It has significant advantages with respect to conventional reflection techniques in that no 10 Kramers-Kronig transformation and related extrapolation of the experimental data to zero and infinite frequency nor reference measurements are required. The subject of the present work are studies of the c-axis dielectric response of the cuprate high Tc superconductors in the far- and mid-infrared spectral ranges. The main topics are (i) the investigation of the Josephson plasma resonances in the so-called three-layer compound Bi2Sr2CaCu3O10?d and the related phonon anomalies which can be described in term of local electric field effects and (ii) the influence of the substitution of non-magnetic Zn and magnetic Ni-impurities on the normal state pseudogap in order to obtain more information about the underlying correlations.

In der vorliegenden Arbeit soll die c-Achsenleitf¨ahigkeit der Kuprat-Hochtemperatur-Supraleiter im Spektralbereich des fernen und des nahen Infrarot untersucht werden. Die Themen sind (i) die Untersuchung der sogenannten Josephson-Plasmonen in der Dreifach-Schichtverbindung d-oder Bi2Sr2CaCu3O10?d und den damit verbundenen Phononenanomalien und (ii) der Einfluss der Substitution von nicht-magnetischen Zn- und von magnetischen Ni- Fehlstellen im Hinblick auf die Pseudoenergielücke im Normalzustand und zugrunde liegenden Korrelationen.