E.V. Gorbar, V.P. Gusynin, and O.O. Sobol, Electron states in the field of charged impurities in two-dimensional Dirac systems (Review Article): , Low Temp. Phys. 44, (2018) [Fiz. Nizk. Temp. 44, 491-524, (2018)] DOI: https://doi.org/10.1063/1.5034149.