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New Breakthrough Transforms Conventional LEDs into Spintronic Devices

In the realm of electronics, traditional devices rely on semiconductors to relay data through electrons and holes, representing binary code as “1s” and “0s.” In contrast, spintronic devices utilize the magnetic orientation of electrons, known as spin, to significantly enhance data processing capabilities. Typically, an “up” spin correlates to a 1, while a “down” spin represents a 0.

However, a significant hurdle in advancing spintronics for commercial applications has been the challenge of establishing and stabilizing electron spin orientation. Many current methods involve the use of ferromagnets and magnetic fields, a complex and often unreliable approach. Research over the years indicates that carriers tend to lose their spin orientation when transitioning through materials of varying conductivity, such as moving from metallic ferromagnets to less conductive semiconductors.

In a groundbreaking development, researchers have successfully converted standard optoelectronic devices into ones capable of controlling electron spin at room temperature, without needing ferromagnets or magnetic fields.

Typically, devices like LEDs manage only electrical charge and light emissions but do not influence electron spin. A collaborative research effort involving physicists from the University of Utah and scientists at the National Renewable Energy Laboratory (NREL) led to the replacement of standard LED electrodes with a patented spin filter composed of a hybrid organic-inorganic halide perovskite material. This innovation resulted in the production of circularly polarized light, demonstrating that the filter effectively injected spin-aligned electrons into the LED’s semiconductor framework—a significant advancement for spintronic technology.

Valy Vardeny, a Distinguished Professor in the Department of Physics & Astronomy at the University of Utah and co-author of the study, expressed excitement about the discovery: “It’s a miracle. For decades, we’ve struggled to inject spin-aligned electrons into semiconductors due to the incompatibility between metallic ferromagnets and non-magnetic semiconductors. This breakthrough will excite the development of devices leveraging both spin and optoelectronics, like spin-LEDs and magnetic memory.”

The findings were published in the journal Nature on June 19, 2024.

Chiral Spin Filters: A Novel Approach

The foundation for this new technology was laid in 2021, when the same research group developed an active spin filter featuring two layers of chiral hybrid organic-inorganic halide perovskites. Chirality refers to the unique symmetry of molecules where one cannot be superimposed onto its mirror image. This concept is observable in everyday objects, like human hands.

Materials with chiral architectures, including DNA and certain perovskite layers, allow for selective electron movement. The spin filter incorporates a “left-handed” chiral layer that permits electrons with “up” spins to pass while blocking those with “down” spins, and vice versa. By implementing this chiral spin filter into conventional optoelectronics, the researchers successfully opened up new avenues for spintronic applications.

“We took an LED from the shelf, swapped one electrode for the spin filter, added another standard electrode, and voilà! The emitted light displayed a high degree of circular polarization,” reported Vardeny.

The fabrication of the spin LEDs involved stacking multiple layers, each designed with specific characteristics. The initial layer serves as a transparent metallic electrode, while the subsequent layer is engineered to block electrons spinning in the incorrect direction, hence functioning as a chirality-induced spin filter. The final active layer facilitates the recombination of spin-aligned electrons, generating photons that spiral along a distinctive path rather than following traditional wave patterns, thereby yielding the LED’s characteristic circularly polarized electroluminescence.

Matthew Beard, co-author from NREL, noted, “This work illustrates the remarkable potential of these emerging hybrid semiconductors to harness and merge the unique properties of both organic and inorganic systems. Here, the chiral aspect is derived from the organic materials, which govern the spin, while the inorganic components enhance conductivity and charge management.”

After integrating the spin filter into the standard LED, Xin Pan, a research assistant in the Department of Physics & Astronomy at the University of Utah, confirmed the successful operation of the device, particularly concerning the injection of spin-aligned electrons. Nevertheless, further investigations are necessary to understand the mechanisms enabling the creation of polarized spins.

Vardeny remarked, “That’s the $64,000 question for theorists. It’s indeed remarkable to achieve this without fully comprehending the underlying processes. The beauty of being an experimentalist is the willingness to try.”

The researchers believe that this inventive technique could be adopted by other scientists utilizing various chiral materials, including DNA, across multiple applications.

More information: Matthew P. Hautzinger et al, Room-temperature spin injection across a chiral perovskite/III–V interface, Nature (2024). DOI: 10.1038/s41586-024-07560-4

Source
phys.org