Detection Of Spin-polarized Electrons Research Articles

Unified Framework for Charge-Spin Interconversion in Spin-Orbit Materials

Materials with spin-orbit coupling are of great interest for various spintronics applications due to the efficient electrical generation and detection of spin-polarized electrons. Over the past decade, many materials have been studied, including topological insulators, transition metals, Kondo insulators, semimetals, semiconductors, and oxides; however, there is no unifying physical framework for understanding the physics and therefore designing a material system and devices with the desired properties. We present a model that binds together the experimental data observed on the wide variety of materials in a unified manner. We show that in a material with a given spin-momentum locking, the density of states plays a crucial role in determining the charge-spin interconversion efficiency, and a simple inverse relationship can be obtained. Remarkably, experimental data obtained over the last decade on many different materials closely follow such an inverse relationship. We further deduce two figure-of-merits of great current interest: the spin-orbit torque (SOT) efficiency (for the direct effect) and the inverse Rashba-Edelstein effect length (for the inverse effect), which statistically show good agreement with the existing experimental data on wide varieties of materials. Especially, we identify a scaling law for the SOT efficiency with respect to the carrier concentration in the sample, which agrees with existing data. Such an agreement is intriguing since our transport model includes only Fermi surface contributions and fundamentally different from the conventional views of the SOT efficiency that includes contributions from all the occupied states.

Field Effect and Spin-Valve Effect in the PbSnTe Topological Crystalline Insulator

The characteristics of MIS structures based on insulating PbSnTe:In films grown by molecular beam epitaxy (MBE) with compositions near the band inversion are studied. It is shown that a number of their features can be induced by a ferroelectric phase transition with the Curie temperature in the range of 15-20 K. The injection and detection of spin-polarized electrons in PbSnTe:In are studied by using ferromagnetic contacts Co and Co $${}_{40}$$ Fe $${}_{40}$$ B $${}_{20}$$ . A spin-valve effect is discovered by measuring the magnetoresistance in local geometry at a distance of more than 30 $$mu$$ m from ferromagnetic contacts. The presence of a surface spin-polarized state with a linear dispersion law is demonstrated by means of the photoemission with angular and spin resolution.

Electric injection and detection of spin-polarized electrons in lateral spin valves on ferromagnetic metal-semiconductor InSb heterojunctions

A lateral spintronic device has been created on the basis of the InSb semiconductor with an iron injector and an iron detector of spin-polarized electrons that are separated from the semiconductor channel by a MgO tunnel barrier. The electric injection and detection of spin-polarized electrons in a single device have been demonstrated. Data on the parameters of the spin subsystem of conduction electrons in the InSb semiconductor and spin polarization of injected electrons in the semiconductor on the Fe/MgO/InSb heterojunction have been obtained from the measurements of the Hanle effect.

All-electrical spin injection and detection in the Co2FeSi/GaAs hybrid system in the local and non-local configuration

We demonstrate the electrical injection and detection of spin-polarized electrons in the Co2FeSi/GaAs hybrid system using lateral transport structures. Spin valve signatures and characteristic Hanle curves are observed both in the non-local and the local configuration. The comparatively large magnitude of the local spin valve signal and the high signal-to-noise ratio are attributed to the large spin polarization at the Fermi energy of Co2FeSi in the well-ordered L21 phase.

Electrical Detection of Spin Transport in Si Using High-quality Fe3Si/Si Schottky Tunnel Contacts

We investigated the epitaxial growth of high-quality Fe3Si thin films on Si(111) and demonstrated electrical injection and detection of spin-polarized electrons in Si through the Fe3Si/Si Schottky-tunnel contacts. TEM observations and analyses of electron diffraction patterns revealed that precisely controlling the Fe/Si ratio during growth is important to obtain well ordered Fe3Si structures and atomically abrupt heterointerfaces at the same time. The electrical properties of Fe3Si/Si Schottky diodes with various carrier concentrations were also examined, and highly transparent tunnel contacts were demonstrated. We were able to clearly detect nonlocal spin signals in Si at 150K using Fe3Si/Si lateral four-probe devices.

Silicon spintronics warms up

Electrical injection and detection of spin-polarized electrons in a silicon chip have now been demonstrated at room temperature, paving the way to the development of low-power semiconductor spintronics circuitry.

Epitaxial growth of a full-Heusler alloy Co 2FeSi on silicon by low-temperature molecular beam epitaxy

For electrical spin injection and detection of spin-polarized electrons in silicon, we explore highly epitaxial growth of ferromagnetic full-Heusler-alloy Co 2FeSi on silicon substrates using low-temperature molecular beam epitaxy (LT-MBE). Although in -situ reflection high energy electron diffraction images clearly show two-dimensional epitaxial growth for growth temperatures ( T G) of 60, 130, and 200 °C, cross-sectional transmission electron microscopy experiments reveal that there are single-crystal phases other than Heusler alloys near the interface between Co 2FeSi and Si for T G = 130 and 200 °C. On the other hand, almost perfect heterointerfaces are achieved for T G = 60 °C. These results and magnetic measurements indicate that highly epitaxial growth of Co 2FeSi thin films on Si is demonstrated only for T G = 60 °C.

Electrical injection and detection of spin-polarized electrons in silicon through an Fe3Si/Si Schottky tunnel barrier

We demonstrate electrical injection and detection of spin-polarized electrons in silicon (Si) using epitaxially grown Fe3Si/Si Schottky-tunnel-barrier contacts. By an insertion of a δ-doped n+-Si layer (∼1019 cm−3) near the interface between a ferromagnetic Fe3Si contact and a Si channel (∼1015 cm−3), we achieve a marked enhancement in the tunnel conductance for reverse-bias characteristics of the Fe3Si/Si Schottky diodes. Using laterally fabricated four-probe geometries with the modified Fe3Si/Si contacts, we detect nonlocal output signals that originate from the spin accumulation in a Si channel at low temperatures.

Electrical spin injection and detection in lateral all-semiconductor devices

Both electrical injection and detection of spin-polarized electrons are demonstrated in a single wafer all-semiconductor GaAs-based lateral spintronic device, employing ${p}^{+}\text{\ensuremath{-}}(\text{Ga},\text{Mn})\text{As}/{n}^{+}$-GaAs ferromagnetic Esaki diodes as spin aligning contacts. Spin-dependent phenomena, such as spin precession and spin-valve effect, are observed in nonlocal signal and the measurements reveal the unusual origin of the latter in the investigated devices. The conversion of spin-polarized holes into spin-polarized electrons via Esaki tunneling leaves its mark in a bias dependence of the spin-injection efficiency, which at maximum reaches the value of 50%.

Direct electronic measurement of the spin Hall effect

The generation, manipulation and detection of spin-polarized electrons in nanostructures define the main challenges of spin-based electronics. Among the different approaches for spin generation and manipulation, spin-orbit coupling--which couples the spin of an electron to its momentum--is attracting considerable interest. In a spin-orbit-coupled system, a non-zero spin current is predicted in a direction perpendicular to the applied electric field, giving rise to a spin Hall effect. Consistent with this effect, electrically induced spin polarization was recently detected by optical techniques at the edges of a semiconductor channel and in two-dimensional electron gases in semiconductor heterostructures. Here we report electrical measurements of the spin Hall effect in a diffusive metallic conductor, using a ferromagnetic electrode in combination with a tunnel barrier to inject a spin-polarized current. In our devices, we observe an induced voltage that results exclusively from the conversion of the injected spin current into charge imbalance through the spin Hall effect. Such a voltage is proportional to the component of the injected spins that is perpendicular to the plane defined by the spin current direction and the voltage probes. These experiments reveal opportunities for efficient spin detection without the need for magnetic materials, which could lead to useful spintronics devices that integrate information processing and data storage.