Electron momentum density studies in high-T_cmaterials by positron annihilation spectroscopy: theory and experiment

Abstract

The authors discuss positron behaviour and in particular the ground state positron probability in high-Tc materials. Special attention is paid to La2CuO4, for which they report detailed high-resolution two-dimensional angular correlation of positron annihilation radiation spectroscopy measurements in three sample orientations and as a function of temperature. Besides a large isotropic core-like electron contribution ( approximately=85%), the remaining anisotropic contribution is attributed to valence electrons which are modelled by a linear combination of atomic orbitals-molecular orbital method in conjunction with a localised ion scheme, within the independent particle model approximation. The covalency structure so derived is used to discuss the case of the parent doped material and YBa2Cu3O7. The authors also comment on the application of the Lock-Crisp-West theorem to La2CuO4, before adding some concluding remarks.