Light-hole states and hyperfine interaction in electrically-defined Ge/GeSn quantum dots

TL;DR

This paper theoretically explores light-hole states and hyperfine interactions in Ge/GeSn quantum dots, revealing how structural parameters and Sn content influence hyperfine coupling and qubit properties.

Contribution

It introduces a detailed atomic-scale model of hyperfine interactions in Ge/GeSn quantum dots, emphasizing the role of Sn content and band mixing in hyperfine coupling.

Findings

Hyperfine coupling strength depends on Sn content in the barrier.

Band mixing introduces s-type admixtures, affecting hyperfine interactions.

Hyperfine interactions are crucial for understanding hole spin qubits in Ge/GeSn QDs.

Abstract

We theoretically investigate hole spins confined in a gate-defined quantum dot (QD) embedded in GeSn/Ge/GeSn quantum well (QW) structure. Owing to the tensile strain in the Ge layer, the system effectively realizes a light-hole qubit. We systematically study how various morphological parameters influence the energy spectrum, g-factors, and the hyperfine coupling to the nuclear spin bath. The simulations are carried out using a realistic, fully atomic sp$^3$d$^5$s$^*$ tight-binding model. We also perform complementary DFT calculations of wave functions near the atomic cores and use them to parameterize the hyperfine-interaction Hamiltonian. We evaluate the Overhauser field fluctuations and demonstrate that the strength of the hyperfine coupling for the lowest hole doublet crucially depends on the Sn content in the barrier. We highlight the conduction-valence band mixing, which leads to considerable $s$-type admixtures to the hole states, providing the dominant channel of hyperfine coupling due to the Fermi contact interaction.