Traditional electronics rely on semiconductors to transmit data using bursts of charged particles (electrons or holes) to convey messages as “1s” and “0s.”
Spintronic devices, however, can handle much more information by using the orientation of electrons’ magnetic poles, known as spin, where an “up” spin represents a 1 and a “down” spin represents a 0.
One major challenge in developing commercial spintronics has been controlling the spin orientation of electrons.
Most devices achieve this using ferromagnets and magnetic fields, a process that is both cumbersome and unreliable.
For years, researchers found that electrons lose their spin orientation when moving from materials with high conductivity, like metallic ferromagnets, to low-conductivity materials, such as undoped silicon or common semiconductor materials.
Now, for the first time, scientists have transformed regular optoelectronic devices into ones that can control electron spin at room temperature, without the need for a ferromagnet or magnetic field.
Most optoelectronic devices, such as LEDs, only control charge and light, not the spin of electrons.
In a groundbreaking study led by physicists from the University of Utah and researchers at the National Renewable Energy Laboratory (NREL), scientists replaced the electrodes of store-bought LEDs with a special spin filter made from hybrid organic-inorganic halide perovskite material.
This new setup enabled the LEDs to produce circularly polarized light, indicating that the filter successfully injected spin-aligned electrons into the LED’s semiconductor structure—a significant advancement for spintronics technology.
“It’s a miracle,” said Valy Vardeny, Distinguished Professor at the University of Utah and co-author of the study. “For decades, we’ve struggled to efficiently inject spin-aligned electrons into semiconductors because of the mismatch between metallic ferromagnets and non-magnetic semiconductors.
This discovery will excite anyone working with spin and optoelectronics, like spin-LEDs or magnetic memory.”
The study, published in Nature, details how the team used a patented spin filter made from chiral hybrid organic-inorganic halide perovskites.
Chirality refers to a molecule’s symmetry, where its mirror image cannot be superimposed on itself, like human hands. In this filter, a “left-handed” chiral layer allows electrons with “up” spins to pass while blocking “down” spins, and vice versa.
“We took a standard LED, replaced one electrode with the spin filter material, and added another regular electrode. Instantly, the light became highly circularly polarized,” explained Vardeny.
Chemists at NREL fabricated the spin LEDs by stacking several layers, each with specific properties. The first layer is a common transparent metallic electrode. The second layer, the chiral spin filter, blocks electrons with the wrong spin direction.
The third layer, a standard semiconductor, recombines the spin-aligned electrons to produce photons that move in a spiral path, creating the LED’s circularly polarized light.
“This work shows the unique and powerful ability of these ‘hybrid’ semiconductors to combine the distinct properties of organic and inorganic systems,” said Matthew Beard, co-author of the study from NREL. “The organic molecules provide spin control, while the inorganic component offers conductivity and charge control.”
Although the exact mechanism behind the polarized spins is not yet fully understood, the researchers are optimistic. “That’s the $64,000 question for a theorist to answer,” said Vardeny. “The beauty of being an experimentalist is that you can make discoveries without fully understanding the underlying mechanisms.”
The team believes that this technique could be applied to other chiral materials, such as DNA, in various contexts, opening new possibilities for spintronic devices.
