Dec 04, 2020 |
Electrical spin filtering the key to ultra-fast, energy-efficient spintronics
(Nanowerk News) Spin-filtering could be the key to faster, more energy-efficient switching in future spintronic technology, allowing the detection of spin by electrical rather than magnetic means.
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A paper published in Physical Review B ("A non-linear spin filter for non-magnetic materials at zero magnetic field") demonstrates spin detection using a spin filter to separate spin orientation according to their energies.
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Ultra-fast, ultra-low energy ‘spintronic’ devices are an exciting, beyond-CMOS technology.
Detecting spin via electrical means in future spintronics
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The emerging field of spintronic devices use the extra degree of freedom offered by particles’ quantum spin, in addition to its charge, allowing for ultra-fast, ultra-low energy computation.
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The key is the ability to generate and detect spin as it accumulates on a material’s surface.
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The aim of researchers is to generate and detect spin via electrical means, rather than magnetic means, because electric fields are a lot less energetically costly to generate than magnetic fields.
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Top: Electron microscope image of the experimental device. Bottom: mapping the non-linear spin signal for different operating conditions. (Image: FLEET)
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Energy-efficient spintronics is dependent on both generation and detection of spin via electrical means.
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In strongly spin-orbit coupled semiconductor systems, all-electrical generation of spin has already been successfully demonstrated.
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However, detection of spin-to-charge conversion has always required a large range of magnetic fields, thus limiting the speed and practicality.
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In this new study, UNSW researchers have exploited the non-linear interactions between spin accumulation and charge currents in gallium-arsenide holes, demonstrating all-electrical spin-to-charge conversion without the need for a magnetic field.
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“Our technique promises new possibilities for rapid spin detection in a wide variety of materials, without using a magnetic field,” explains lead author Dr Elizabeth Marcellina.
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Previously, generation and detection of spin accumulation in semiconductors has been achieved through optical methods, or via the spin Hall effect-inverse spin Hall effect pair.
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However, these methods require a large spin diffusion length, meaning that they are not applicable to strongly spin-orbit coupled materials with short spin diffusion length.
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All-electrical spin filtering
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The UNSW study introduces a new method for detecting spin accumulation—using a spin filter, which separates different spin orientations based on their energies.
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Typically, spin filters have relied on the application of large magnetic fields, which is impractical and can interfere with the spin accumulation.
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Instead, the UNSW team exploited non-linear interactions between spin accumulation and charge, which facilitate the conversion of spin accumulation into charge currents even at zero magnetic field.
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“Using ballistic, mesoscopic gallium-arsenide holes as a model system for strongly spin-orbit coupled materials, we demonstrated non-linear spin-to-charge conversion that is all-electrical and requires no magnetic field,” says corresponding author A/Prof Dimi Culcer (UNSW).
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“We showed that non-linear spin-to-charge conversion is fully consistent with the data obtained from linear response measurements and is orders of magnitude faster,” says corresponding-author Prof Alex Hamilton, also at UNSW.
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Because the non-linear method does not need a magnetic field nor a long spin diffusion length, it promises new possibilities for fast detection of spin accumulation in strongly spin-orbit coupled materials with short spin diffusion lengths, such as TMDCs and topological materials.
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Finally, the rapidness of non-linear spin-to-charge conversion can enable time-resolved read-out of spin accumulation down to 1 nanosecond resolution.
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