Electronic bound states around charged impurities in two-dimensional systems with structural inversion asymmetry can be described in terms of a two-dimensional hydrogen atom in the presence of a Rashba spin-orbit interaction. Here, the energy levels of the bound electron are evaluated numerically as a function of the spin-orbit interaction, and analytic expressions for the weak and strong spin-orbit coupling limits are compared with the numerical results. It is found that, besides the level splitting due to the lack of inversion symmetry, the energy levels are lowered for sufficiently strong spin-orbit coupling, indicating that the electron gets more tightly bound to the ion as the spin-orbit interaction increases. Similarities and differences with respect to the two-dimensional Fröhlich polaron with Rashba coupling are discussed.PACS numbers: 71.70. Ej, 73.21.Fg, 73.20.Hb The two-dimensional (2D) hydrogen atom, i. e., an electron constrained to move in a plane and subjected to an attractive Coulomb potential, 1,2,3,4,5 is a theoretical construction which, besides being of interest in itself, has also important physical realizations. It can describe indeed the effect of a charged impurity in 2D systems such as quantum wells and surface states, or in extremely anisotropic three-dimensional crystals, 1 as well as excitons in semiconductor 2D heterostructures.
5The spin-orbit (SO) interaction, arising from the structural and/or bulk inversion asymmetries, characterizes several of the above mentioned low-dimensional systems, 6 and gives rise to energy level splittings ranging from a few to hundreds of meV, depending on the material characteristics (see for example Ref. [7]). Furthermore, the possibility of tuning the SO interaction in semiconductor quantum wells by means of external applied voltages represents the key feature for application in spintronics. Given this situation, it becomes therefore natural to assess how the properties of a 2D hydrogen atom are affected by the SO interaction.Several studies have already been devoted to the effect of the SO coupling in electrons interacting with central potentials, such as those describing hard-wall or parabolic quantum dots. 8,9,10,11,12 However, despite its potential interest for SO coupled low-dimensional systems, the specific 2D Coulomb problem appears to have been only marginally considered in the literature.12 In this Brief Report, the 2D Coulomb problem is numerically solved for an electron interacting with a Rashba potential, that is the SO coupling arising from structural inversion asymmetry in the direction perpendicular to the 2D plane.13 It is found that the Rashba interaction removes partially the initial degeneracy of the 2D hydrogen atom, and the resulting energy levels are two-fold degenerate due to the time-reversal invariance of the model. Furthermore, it is shown that the SO interaction renders the electron more tightly bound to the ion, confirming a general trend observed for other central potentials and for 2D electrons coupled to phonons.The ...