Ground state and polarization of an hydrogen-like atom near a Weyl semimetal

Abstract

In this paper we study the effects of a topological Weyl semimetal (WSM) upon the ground state and polarization of an hydrogen-like atom near its surface. The WSM is assumed to be in the equilibrium state and at the neutrality point, such that the interaction between the atomic charges and the material is fully described (in the non retarded regime) by axion electrodynamics, which is an experimentally observable signature of the anomalous Hall effect in the bulk of the WSM. The atom-WSM interaction provides additional contributions to the Casimir-Polder potential thus modifying the energy spectra and wave function, which now became distance dependent. Using variational methods, we solve the corresponding Schrödinger equation for the atomic electron. The ground state and the polarization are analyzed as a function of the atom-surface distance, and we directly observe the effects of the nontrivial topology of the material by comparing our results with that of a topologically trivial sample. We also study the impact of the medium's permittivity by assuming a hydrogen atom in vacuum and a donor impurity in gallium arsenide (GaAs). We found that the topological interaction behaves as an effective-attractive charge so that the electronic cloud tends to be polarized to the interface of materials. Moreover, the loss of wave-function normalization is interpreted as a critical location from below which the bound state is broken.

Electromagnetic coupling and transport in a topological insulator-graphene hetero-structure

“…In addition, the so-called magneto-electric polarizability (MEP) [8,9] that locally modifies the constitutive relations between the electromagnetic fields in TIs, provides new opportunities to control the magnetoelectric response in such systems. Even though these effects have been extensively studied in individual topological materials, their electromagnetic coupling when integrated into hetero-structures remains a vast territory for further exploration [10,11].…”