Electron Doping in FeSe Monolayer and Multilayer via Metal Phthalocyanine Adsorption: A First-principle Investigation

Electron doping has been established as an effectively method to enhance the superconducting transition temperature and superconducting energy gap of FeSe thin films on strontium titanate (SrTiO3) substrates. Previous studies have demonstrated that electron/hole doping can be achieved through the adsorption of metal phthalocyanine (MPc, M = Co, Cu, Mn, Fe, and Ni) molecules on surfaces. This work explores the electron doping induced by the adsorption of MPc molecules, specifically cobalt phthalocyanine (CoPc) and copper phthalocyanine (CuPc), onto FeSe monolayer and multilayers. Utilizing first-principle calculations based on density functional theory, we demonstrate that charge rearrangement occurs when MPc molecules adsorb on the FeSe substrate, contributing to an accumulation of electrons at the interface. In the CoPc/FeSe systems, the electron accumulation increases with the layer number of FeSe substrate, converging for substrates with 3-5 layers. The analysis of integrated planar charge difference up to the position with zero integrated charge transfer reveals that the all the five MPc molecules donate electrons to the uppermost FeSe layer. The electron donation suggests that MPc adsorption can be a promising strategy to modulate the superconductivity of FeSe layers.