Effect of Local Electron-Electron Correlation in Hydrogen-like Impurities in Ge

TL;DR

This study investigates how local electron-electron interactions influence the electronic and magnetic properties of hydrogen impurities in germanium, revealing conditions for magnetic activity and potential electrical behavior.

Contribution

It introduces a combined empirical tight binding and dynamical mean field theory approach to analyze impurity states beyond local density approximation limitations.

Findings

Local moments emerge in strong interaction regimes

Spectral density indicates possible electrical activity near the gap

Impurity properties depend on Coulomb interaction and hopping parameters

Abstract

We have studied the electronic and local magnetic structure of the hydrogen interstitial impurity at the tetrahedral site in diamond-structure Ge, using an empirical tight binding + dynamical mean field theory approach because within the local density approximation (LDA) Ge has no gap. We first establish that within LDA the 1s spectral density bifurcates due to entanglement with the four neighboring sp3 antibonding orbitals, providing an unanticipated richness of behavior in determining under what conditions a local moment hyperdeep donor or Anderson impurity will result, or on the other hand a gap state might appear. Using a supercell approach, we show that the spectrum, the occupation, and the local moment of the impurity state displays a strong dependence on the strength of the local on-site Coulomb interaction U, the H-Ge hopping amplitude, the depth of the bare 1s energy level epsilon_H, and we address to some extent the impurity concentration dependence. In the isolated impurity, strong interaction regime a local moment emerges over most of the parameter ranges indicating magnetic activity, and spectral density structure very near (or in) the gap suggests possible electrical activity in this regime.