Giant g factor tuning of long-lived electron spins in Ge

TL;DR

This paper demonstrates that by engineering quantum wells of germanium on silicon substrates, one can achieve long electron spin coherence times and tune the g factor and its anisotropy, advancing spintronics in CMOS-compatible platforms.

Contribution

The study reveals a method to control the g factor and spin coherence in Ge/Si heterostructures, overcoming previous limitations and enabling scalable spintronic devices.

Findings

Long spin relaxation and coherence times in Ge quantum wells.

Tunable g factor and anisotropy via quantum confinement.

Potential for CMOS-compatible spintronic applications.

Abstract

Control of electron spin coherence via external fields is fundamental in spintronics. Its implementation demands a host material that accommodates the highly desirable but contrasting requirements of spin robustness to relaxation mechanisms and sizeable coupling between spin and orbital motion of charge carriers. Here we focus on Ge, which, by matching those criteria, is rapidly emerging as a prominent candidate for shuttling spin quantum bits in the mature framework of Si electronics. So far, however, the intrinsic spin-dependent phenomena of free electrons in conventional Ge/Si heterojunctions have proved to be elusive because of epitaxy constraints and an unfavourable band alignment. We overcome such fundamental limitations by investigating a two dimensional electron gas (2DEG) confined in quantum wells of pure Ge grown on SiGe-buffered Si substrates. These epitaxial systems demonstrate exceptionally long spin relaxation and coherence times, eventually unveiling the potential of Ge in bridging the gap between spintronic concepts and semiconductor device physics. In particular, by tuning spin-orbit interaction via quantum confinement we demonstrate that the electron Land\'e g factor and its anisotropy can be engineered in our scalable and CMOS-compatible architectures over a range previously inaccessible for Si spintronics.