Abstract
The Rashba and Dresselhaus spin-orbit (SO) interactions in 2D electron gases act as effective magnetic fields with momentum-dependent directions, which cause spin decay as the spins undergo arbitrary precessions about these randomly oriented SO fields due to momentum scattering. Theoretically and experimentally, it has been established that by fine-tuning the Rashba and renormalized Dresselhaus couplings to equal fixed strengths , the total SO field becomes unidirectional, thus rendering the electron spins immune to decay due to momentum scattering. A robust persistent spin helix (PSH), i.e., a helical spin-density wave excitation with constant pitch , , has already been experimentally realized at this singular point , enhancing the spin lifetime by up to 2 orders of magnitude. Here, we employ the suppression of weak antilocalization as a sensitive detector for matched SO fields together with independent electrical control over the SO couplings via top gate voltage and back gate voltage to extract all SO couplings when combined with detailed numerical simulations. We demonstrate for the first time the gate control of the renormalized and the continuous locking of the SO fields at ; i.e., we are able to vary both and controllably and continuously with and , while keeping them locked at equal strengths. This makes possible a new concept: “stretchable PSHs,” i.e., helical spin patterns with continuously variable pitches over a wide parameter range. Stretching the PSH, i.e., gate controlling while staying locked in the PSH regime, provides protection from spin decay at the symmetry point , thus offering an important advantage over other methods. This protection is limited mainly by the cubic Dresselhaus term, which breaks the unidirectionality of the total SO field and causes spin decay at higher electron densities. We quantify the cubic term, and find it to be sufficiently weak so that the extracted spin-diffusion lengths and decay times show a significant enhancement near . Since within the continuous-locking regime quantum transport is diffusive (2D) for charge while ballistic (1D) for spin and thus amenable to coherent spin control, stretchable PSHs could provide the platform for the much heralded long-distance communication between solid-state spin qubits, where the spin diffusion length for is an order of magnitude smaller.
- Received 16 February 2017
DOI:https://doi.org/10.1103/PhysRevX.7.031010
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Future quantum technologies envision the use of an electron’s spin as a means of storing and manipulating information. Interactions between an electron spin and its orbital motion offer an attractive method for controlling the orientation of the spin using electric fields. So far, the applicability of this technique has been limited by spin dephasing, where the spins of many electrons decay over time. We experimentally demonstrate a new method for controlling spin orientation on a chip while avoiding randomization.
Our method generates conditions on a chip so that a spin with some initial polarization, moving from an injector to a detector, performs well-defined rotations without decaying. These rotations depend only on the distance traveled. Along this path, the spin orientation forms a wavelike pattern, a so-called spin helix. By changing gate voltages on the chip we can stretch the helix pattern by stretching its wavelength, thus manipulating the spin orientation at the detector. We achieve this by independently tuning the two main contributions of the spin-orbit interaction, the Rashba and Dresselhaus fields. To control the spin we can keep the ratio of these fields locked to unity and change only their overall strength. This effectively stretches the spin-helix length (the distance for one full rotation of the spin) and enables in situ control of the spin orientation as well as the controlled transfer of the spin polarization over long distances.
We believe that our method could enable a new generation of devices such as spin field-effect transistors, quantum communication channels, quantum dots, and Skyrmion lattices—also in semiconductor materials other than gallium arsenide—and motivate future experimental work in a broad range of condensed-matter topics.