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Register a new userEfficient spin transport along Si $langle$100$rangle$ at room temperature
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We find efficient spin transport in Si at room temperature in lateral spin valves (LSVs). When the crystal orientation of the spin-transport channel in LSVs is changed from $langle$110$rangle$, which is a conventional cleavage direction, to $langle$100$rangle$, the maximum magnitude of the spin signals is markedly enhanced. From the analyses based on the one-dimensional spin diffusion model, we can understand that the spin injection/detection efficiency in Si$langle$100$rangle$ LSVs is larger than that in Si$langle$110$rangle$ ones. We infer that, in Si-based LSVs, the spin detection efficiency of the pure spin current is related to the crystallographic orientation of the valley structures of the conduction band in Si.
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The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport also supercurrent transport has already been observed. It has also been suggested that graphene might be a promising material for spintronics and related applications, such as the realization of spin qubits, due to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. As a first step in the direction of graphene spintronics and spin qubits we report the observation of spin transport, as well as Larmor spin precession over micrometer long distances using single graphene layer based field effect transistors. The non-local spin valve geometry was used, employing four terminal contact geometries with ferromagnetic cobalt electrodes, which make contact to the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals which reflect the magnetization direction of all 4 electrodes, indicating that spin coherence extends underneath all 4 contacts. No significant changes in the spin signals occur between 4.2K, 77K and room temperature. From Hanle type spin precession measurements we extract a spin relaxation length between 1.5 and 2 micron at room temperature, only weakly dependent on charge density, which is varied from n~0 at the Dirac neutrality point to n = 3.6 10^16/m^2. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around 10%.
Spin transport in non-degenerate semiconductors is expected to pave a way to the creation of spin transistors, spin logic devices and reconfigurable logic circuits, because room temperature (RT) spin transport in Si has already been achieved. However, RT spin transport has been limited to degenerate Si, which makes it difficult to produce spin-based signals because a gate electric field cannot be used to manipulate such signals. Here, we report the experimental demonstration of spin transport in non-degenerate Si with a spin metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We successfully observed the modulation of the Hanle-type spin precession signals, which is a characteristic spin dynamics in non-degenerate semiconductor. We obtained long spin transport of more than 20 {mu}m and spin rotation, greater than 4{pi} at RT. We also observed gate-induced modulation of spin transport signals at RT. The modulation of spin diffusion length as a function of a gate voltage was successfully observed, which we attributed to the Elliott-Yafet spin relaxation mechanism. These achievements are expected to make avenues to create of practical Si-based spin MOSFETs.
To mitigate climate change, our global society is harnessing direct (solar irradiation) and indirect (wind/water flow) sources of renewable electrical power generation. Emerging direct sources include current-producing thermal gradients in thermoelectric materials, while quantum physics-driven processes to convert quantum information into energy have been demonstrated at very low temperatures. The magnetic state of matter, assembled by ordering the electrons quantum spin property, represents a sizeable source of built-in energy. We propose to create a direct source of electrical power at room temperature (RT) by utilizing magnetic energy to harvest thermal fluctuations on paramagnetic (PM) centers. Our spin engine rectifies current fluctuations across the PM centers spin states according to the electron spin by utilizing so-called spinterfaces with high spin polarization. As a rare experimental event, we demonstrate how this path can generate 0.1nW at room temperature across a 20 micron-wide spintronic device called the magnetic tunnel junction, assembled using commonplace Co, C and MgO materials. The presence of this path in our experiment, which also generates very high spintronic performance, is confirmed by analytical and ab-initio calculations. Device downscaling, and the ability for other materials systems than the spinterface to select a transport spin channel at RT widens opportunities for routine device reproduction. The challenging control over PM centers within the tunnel barriers nanotransport path may be addressed using oxide- and organic-based nanojunctions. At present densities in MRAM products, this spin engine could lead to always-on areal power densities well beyond that generated by solar irradiation on earth. Further developing this concept can fundamentally alter our energy-driven societys global economic, social and geopolitical constructs.
We report the observation of spin-to-charge current conversion in strained mercury telluride at room temperature, using spin pumping experiments. The conversion rates are found to be very high, with inverse Edelstein lengths up to 2.0 +/- 0.5 nm. The influence of the HgTe layer thickness on the conversion efficiency has been studied, as well as the role of a HgCdTe barrier inserted in-between the HgTe and NiFe layers. These measurements, associated to the temperature dependence of the resistivity, allows to ascribe these high conversion rates to the spin momentum locking property of HgTe surface states.
Semiconductor light emitters compatible with standard Si integration technology (SIT) are of particular interest for overcoming limitations in the operating speed of microelectronic devices 1-3. Light sources based on group-IV elements would be SIT compatible but suffer from the poor optoelectronic properties of bulk Si and Ge. Here, we demonstrate that epitaxially grown Ge quantum dots (QDs) in a fully coherent Si matrix show extraordinary optical properties if partially amorphised by Ge-ion bombardment (GIB). The GIB-QDs exhibit a quasi-direct-band gap and show, in contrast to conventional SiGe nanostructures, almost no thermal quenching of the photoluminescence (PL) up to room-temperature (RT). Microdisk resonators with embedded GIB-QDs exhibit threshold-behaviour and super-linear increase of the integrated PL-intensity (IPL) with increasing excitation power Pexc which indicates light amplification by stimulated emission in a fully SIT-compatible group-IV nano-system.
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