A first-principles study on electronic structure and crystal field effect of layered La2CuO4 as composed of CuO2 and La2O2 monolayers

Since the exact mechanism of superconductivity has not been completely understood yet, investigating this phenomenon is of great interest. Here, we first studied CuO2 and La2O2 monolayers separately and then investigated the changes in the electronic structure of the layered La2CuO4 as formed by stacking those monolayers together. The results showed that when the two layers are sandwiched in tandem, a charge transfer mechanism occurs initially from La2O2 to CuO2. This charge transfer mechanism results in localized orbitals that contribute to the bonds in CuO2, making them stronger. On the other hand, Cu dz2 orbitals move toward the Fermi level, being more delocalized. This phenomenon occurs by changing the crystal field effect on Cu atoms and creating the octahedral coordination of O atoms around Cu atoms. Therefore, due to the crystal field effect, the energy level of dz2 orbitals, which lie under those of dxz + dyz and dxy orbitals, ascend and lie under the energy level of dx2y2 orbitals. These changes in the electronic structure create a half-filled band around the Fermi level consisted of Cu dx2y2 and dz2 orbitals and apical O Pz orbitals. This configuration occurs by emptying the states due to La2O2 near the Fermi level and occupying the states due to CuO2, lowering the bands in energy. The lowering separates the band around the Fermi level from other bands.

Automated summary

The study examined the electronic structure changes in CuO2 and La2O2 monolayers and the layered La2CuO4 when stacked together. It was found that a charge transfer mechanism occurs when sandwiched together, resulting in adjustments to the electronic structure of CuO2 due to charge transfer from La2O2. This led to the creation of a half-filled band around the Fermi level consisting of Cu dx2y2 and dz2 orbitals and apical O Pz orbitals.