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

TL;DR

This study investigates how a Weyl semimetal influences the ground state and polarization of a nearby hydrogen-like atom, revealing topological effects on atomic properties through modifications in the Casimir-Polder potential.

Contribution

It introduces a variational approach to analyze atomic states near a Weyl semimetal, highlighting the impact of topological axion electrodynamics on atomic spectra and polarization.

Findings

Topological interactions act as an effective attractive charge.

The atomic wave function can break down at a critical distance.

Polarization of the electronic cloud is directed towards the interface.

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 Schr\"{o}dinger 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 the semiconductors gallium arsenide (GaAs) and gallium phosphide (GaP). 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.