Shining light on the electronic structure of the high critical temperature superconductors.

摘要

The excitement following the discovery of high-temperature superconductivity was shared between those who finally saw an opportunity to take advantage of the unique properties of a superconductor at an economical price and those who wondered why metal oxides, normally good insulators, would superconduct at temperatures higher than thought possible for metals and alloys. It was soon revealed that even in the normal state, the cuprates exhibit very unusual physical properties.; To investigate the origin of the unusual normal state properties and shed light on the superconducting mechanism, we used angle resolved photoemission spectroscopy to study the electronic structure of the high-T{dollar}sb{lcub}rm c{rcub}{dollar} superconductors. We focused on Bi{dollar}sb2{dollar}Sr{dollar}sb2{dollar}CuO{dollar}sb6{dollar}, Nd{dollar}sb{lcub}rm 2-x{rcub}{dollar}Ce{dollar}sb{lcub}rm x{rcub}{dollar}CuO{dollar}sb{lcub}4+delta{rcub}{dollar}, and Sr{dollar}sb2{dollar}CuO{dollar}sb2{dollar}Cl{dollar}sb2{dollar}, all single layer cuprates, so we could unambiguously study the electronic structure of the crucial CuO{dollar}sb2{dollar} plane, where the superconducting carriers are known to travel. We succeeded in revealing a number of fascinating features in the electronic structure, including band-like Fermi surfaces, flat band saddle points, and nested Fermi surface sections. This data has been used to explain many aspects of the unusual normal state properties. In addition, by looking at the electronic structure at different doping regimes, under-doped insulating, optimally-doped superconducting, and over-doped metallic, we found that many features, previously thought explainable only by one-electron band theory, may be better understood by a many-body approach. Furthermore, other properties of the high-T{dollar}sb{lcub}rm c{rcub}{dollar} superconductors, which are difficult to understand with band theory, are well described using a many-body picture.