Abstract
We have measured the insulating energy gap Δ and the exchange interaction J in a series of cuprate crystals, including T’-phase (M=Pr, Nd, Sm, Eu, and Gd), -phase La,Tb,, and T-phase . We find that the energy gap scales predominantly with the in-plane Cu-O distance, scaling as δ logΔ/ δ logd∼-6. Furthermore, contrary to simple expectations, the energy gap increases with decreasing Cu-O distance, suggesting that Coulomb and other repulsive energies dominate the effects of band hybridization. Using a three-band Hubbard-model expression, our studies of Δ and J in the cuprates allow us to estimate that the hopping energy t scales with Cu-O distance as δ logt/δ logd∼-4.
- Received 12 June 1990
DOI:https://doi.org/10.1103/PhysRevB.42.10785
©1990 American Physical Society