Abstract
Control of electron spin coherence via external fields is fundamental in spintronics. Its implementation demands a host material that accommodates the desirable but contrasting requirements of spin robustness against relaxation mechanisms and sizeable coupling between spin and orbital motion of the carriers. Here, we focus on Ge, which is a prominent candidate for shuttling spin quantum bits into the mainstream 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 these fundamental limitations by investigating a two-dimensional electron gas in quantum wells of pure Ge grown on Si. These epitaxial systems demonstrate exceptionally long spin lifetimes. In particular, by fine-tuning quantum confinement we demonstrate that the electron Landé g factor can be engineered in our CMOS-compatible architecture over a range previously inaccessible for Si spintronics.
Highlights
Control of electron spin coherence via external fields is fundamental in spintronics
In light of the pivotal advances reported in the field of Si photonics[40,41] we expect that band-gap engineering in SiGe alloys will provide advantages to semiconductor spintronics by opening unexplored pathways for the full exploitation of Ge
This, combined with conduction electron spin resonance (CESR), permits experimental detection of the electron g factor theoretically predicted in Ge more than a decade ago[42]
Summary
Control of electron spin coherence via external fields is fundamental in spintronics. Spin–orbit interaction (SOI) couples the quasi-momentum of charged particles to their spin[1] This effect has sparked considerable interest because it results in a suitable spin splitting even in the absence of external magnetic fields. SOI governs spin-dependent phenomena such as Rashba physics[2,3,4,5,6], persistent spin helix states[7,8,9], spin Hall[10,11,12] and spin Seebeck effects[13,14], offering novel and exciting perspectives for utilizing spin currents in non-magnetic materials[15] This holds the promise for the end-of-the-roadmap implementation of semiconductor spintronics[16]. In view of its full compatibility with the technology of integrated circuits and its exceptionally high bulk mobility, Ge increasingly is seen as a viable option for replacing Si in conventional high-frequency logics[32] and can be regarded as an attractive candidate for transport in novel spintronic architectures
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