EPL, 87 (2009) 67005
DOI: 10.1209/0295-5075/87/67005

Real-space fluctuations of effective exchange integrals in high-T_c cuprates

S. Petit and M.-B. Lepetit

CRISMAT, ENSICAEN-CNRS UMR6508 - 6 bd. Maréchal Juin, 14050 Caen, France, EU

received 9 July 2009; accepted in final form 10 September 2009; published September 2009
published online 8 October 2009

Abstract
We present ab initio calculations of effective magnetic exchange, J, as well as Hubbard parameters (t, U and ) as a function of the local distribution of doping atoms for the high-T_c superconducting (Ca_xLa_1-x)(Ba_1.75-xLa_0.25+x)Cu₃O_y family. We found that both the exchange and the energies of the magnetic orbitals are strongly dependent on the local dopant distribution, both through the induced modification of the apical oxygen location and of the induced local electrostatic potential. The J real-space map, for a random distribution of dopants, positively compares with observed STS gap inhomogeneity maps. Similarly, the orbital energy fluctuations induce weak charge inhomogeneities on copper sites, that can be positively compared with the observed LDOS inhomogeneities. These results clearly support an extrinsic origin of both the gap inhomogeneities and LDOS.

PACS
74.62.Dh - Effects of crystal defects, doping and substitution.
75.30.Et - Exchange and superexchange interactions.
71.10.Fd - Lattice fermion models (Hubbard model, etc.).

© EPLA 2009