Two-photon momentum density in La2−xSrxCuO4 and Nd2−xCexCuO4

Abstract

We present calculations of the electron-positron momentum density for the high-${\mathit{T}}_{\mathit{c}}$ superconductors ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ and ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$, together with experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) for ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$. The calculations are based on first-principles electronic structure obtained using the full-potential linearized augmented-plane-wave and the linear muffin-tin orbital methods. Our results indicate a non-negligible overlap of the positron wave function with the ${\mathrm{CuO}}_2$ plane electrons responsible for the Fermi surfaces in these compounds. Therefore, these compounds may be well suited for investigating Fermi-surface-related effects. After the folding of umklapp terms according to Lock, Crisp, and West, the predicted Fermi-surface breaks are mixed with strong effects induced by the positron wave function in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$, while their resolution is better in ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$. A comparison of our calculations with the most recent experimental results for ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ shows good agreement. For ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ good agreement is observed between theoretical and experimental 2D-ACAR profiles.