ROLE OF CU-O LINEAR-CHAINS IN HIGH-TEMPERATURE SUPERCONDUCTIVITY AND ANTIFERROMAGNETISM IN YBA2CU3O7-DELTA

We present briefly the main results of our electronic structure calculations for the high T//c compound YBa//2Cu//3O//7 and the closely-related non-superconducting compound YBa//2Cu//3O//6 in which the oxygen atoms from the linear chains are missing. We find that the linear chain Cu atom and the bridging oxygens with which it interacts are, in the non-superconducting compound, in their fully non-conducting Cu** plus and O**2** minus states respectively, allowing no conduction either in the basal plane of the linear chain Cu atom or along the c-axis. This effectively decouples the two-dimensional planes from each other completely, and makes the non-superconducting YBa//2Cu//3O//6 very similar to its sister compound La//2CuO//4. A comparison with the La//2CuO//4 family of compounds would suggest that if a suitable substitution does not result in superconductivity at relatively high temperatures, then the linear chains are vital for high temperature superconductivity.