The Doping Dependence of the Optical Properties of High-Temperature Super-Conductors

Abstract

<p>The phenomenon of high-temperature superconductivity (HTSC) is one of the most intensively studied ones in the modern condensed matter physics. The initial drive to produce a room-temperature superconductor led to the discovery of completely new physics, that can not be explained by the existing theories. This includes not only the properties of HTSC materials in the superconducting state but in the normal state as well. I fact, much of the current research effort is aimed at the understanding of the unconventional normal-state properties of HTSC materials, in a hope that this understanding will unlock the mystery of the superconductivity phenomenon.</p> <p>The superconducting transition temperature of a HTSC material can be changed by chemical doping. While at the initial stages of the HTSC research the research effort was focused on the so-called "optimal" doping regime, the one with a highest superconducting transition temperature, recently attention has begun shifting towards the whole doping range.</p> <p>The work, results of which are presented in this thesis, is aimed at the understanding of the doping dependence of the optical properties of the high-temperature superconducting materials. In particular, we are interested in the infrared energy range since it provides a wealth of information about the low-energy electronic excitations. Mostly the normal-state properties were studied. Several materials studied in this work allowed us to cover the whole metallic doping range of HTSC. The main emphasis of the work presented in this thesis is, however, the "overdoped" regime, where the transition temperature decreases as the material becomes a better metal. This part of the HTSC phase diagram was largely ignored before. We believe therefore, that the new results, presented in this thesis, are an important contribution to the general effort in the field of high-temperature superconductivity research.</p>