Ionic functionalization of many layered materials by alkali and alkaline earth metals enables tuning of the charge carrier density into the superconducting regime. We have investigated their electronic band structure and spectral function with high-resolution angle-resolved photoemission spectroscopy (ARPES). For Ca doped graphene this charge transfer induces a relatively large electron-phonon coupling constant of about 0.4, providing experimental support for the possibility to achieve superconductivity in graphene at 1.5K . Indeed, superconductivity in Ca doped monolayer graphene was realized experimentally only recently .
We have also investigated the interaction of alkali metals with black phosphorous (BP). Based on our recent combined ARPES and ab initio work , we predicted alkali metal doped BP to be superconducting which was indeed found experimentally very recently .
Here we discuss the possibility of observing superconductivity in a topologically protected band in BP. Using ARPES we demonstrate a way of achieving band inversion in BP between the valence and conduction band by giant staggered electric fields induced by the alkali adsorption on surface. Our ARPES results are discussed in relation to theoretical predictions of topologically protected band crossings in black phosphorous.
 A.V. Fedorov et al., Nat. Commun. 5, 3257 (2014).
 J. Chapman et al., Sci. Rep. 6, 23254 (2016).
 A. Sanna et al., 2D Mater. 3, 025013 (2016).
 R. Zhang et al., Nat. Commun. 8, 15036 (2017).