THEORY OF HIGH TEMPERATURE SUPERCONDUCTIVITY IN LANTHANUM CUPRATES: INTERPLAY OF JAHN-TELLER AND MOTT-PHYSICS

Abstract

In January of 1986 George Bednorz and Alex Muller discovered high temperature superconductivity in copper oxides with motivation that higher superconducting transition temperatures Tc could be achieved by combining Jahn-Teller active Cu ions with the structural complexity of layer-type perovskite oxides [l]. Their discovery, honored by the Nobel physics prize a year later, marked an historic milestone in the fields of not only superconductivity but also condensed matter science. In particular, the idea of Jahn-Teller poralon developed by Alex Muller has brought the remarkable development of the Jahn-Teller physics. On the other hand, strong electron correlation also plays an important role in undoped cuprates, suggesting an important role of Mott physics developed by Sir Nevi11 Mott in cuprates. In this paper we would like to show that the interplay between his idea of Jahn-Teller physic and Mott physics plays an essential role in determining the electronic structures and properties of cuprates in their normal and superconducting phases. Let us start with Jahn-Teller physics advocated by Muller. Paying an attention to the CuOs octahedrons in La2Cu04 elongated along the c-axis by the Jahn-Teller interaction, most of theoretical models have considered that the doped holes itinerate through an orbital extended over a CuOz plane. We call these models “a single-component scenario theory”. Since undoped La2Cu04 is an antiferromagnetic insulator, some of the single-component scenario theories pointed out that the electron-correlation is very important in cuprates and that the superconductivity occurs in doped Mott insulators near the metal-insulator transition. Those models, however, have met a serious difficulty that, in the