Theoretical analysis of the Jahn-Teller effect in the La-Ba-Cu-O superconductor

Abstract

We just commemorated the 10 years anniversary of the discovery of the high T-c superconductivity of Bednorz and Muller (BM). In their celebrated paper BM mentioned the possible role of the Jahn-Teller (JT) effect in the enhancement of the transition temperature to the superconducting state. In the present work we analize, under the quasi-molecular approximation, the conditions for the existence of the JT effect in the CuO6 cluster belonging to the La-Ba-Cu-O superconductor of BM. The electronic part is obtained from self consistent ab initio calculations and the force constants are calculated taking the second derivatives of the energy using the Hartree-Fock approximation for the electronic part. Both, the electronic and vibrational parts are classified accordingly to the irreducible representations of the D-4h group in order to establish the JT theorem. The physical consecuences of the presence of the JT effect in CuO6 cluster are discussed.