Organic self-assembled monolayers on superconducting NbSe₂: Interfacial electronic structure and energetics

While organic self-assembled monolayers (SAMs) have been widely used to modify the work function of metal and metal-oxide surfaces, their application to tune the critical temperature of a superconductor has only been considered recently when SAMs were deposited on NbSe2 monolayers (Calavalle et al 2021 Nano Lett. 21 136-143). Here, we describe the results of density functional theory calculations performed on the experimentally reported organic/NbSe2 systems. Our objectives are: (i) to determine how the organic layers impact the NbSe2 work function and electronic density of states; (ii) to understand the possible correlation with the experimental variations in superconducting behavior upon SAM deposition. We find that, upon adsorption of the organic monolayers, the work-function modulation induced by the SAM and interface dipoles is consistent with the experimental results. However, there occurs no significant difference in the electronic density of states near the Fermi level, a consequence of the absence of any charge transfer across the organic/NbSe2 interfaces. Therefore, our results indicate that it is not a SAM-induced tuning of the NbSe2 density of states near the Fermi level that leads to the tuning of the superconducting critical temperature. This calls for further explorations, both experimentally and theoretically, of the mechanism underlying the superconducting critical temperature variation upon formation of SAM/NbSe2 interfaces.