A team of physicists led by Dr. Yuan Lu from the Université de Lorraine’s Institut Jean Lamour has used electrical pulses to manipulate magnetic information into a polarized light signal — a discovery that could revolutionize long-distance optical telecommunications, including between Earth and Mars. The breakthrough involves the field of spintronics, which aims to manipulate the spin of electrons in order to store and process information.
Structure of SOT spin-LED: controlling the intensity of emitted light and charge current is the basis of transferring and processing information; by contrast, robust information storage and magnetic random-access memories are implemented using the spin of the carrier and the associated magnetization in ferromagnets; the missing link between the respective disciplines of photonics, electronics and spintronics is to modulate the circular polarization of the emitted light, rather than its intensity, by electrically controlled magnetization; Dainone et al. demonstrated that this missing link is established at room temperature and zero applied magnetic field in light-emitting diodes through the transfer of angular momentum between photons, electrons and ferromagnets. Image credit: Dainone et al., doi: 10.1038/s41586-024-07125-5.
In spintronics, which has been used successfully in magnetic computer hard drives, information is represented by electron spin and, by its proxy, the direction of magnetization.
Ferromagnets, such as iron or cobalt, have an unequal number of electrons whose spins are oriented either along or against the magnetization axis.
Electrons with spin along the magnetization travel smoothly across a ferromagnet, while those with opposite spin orientation are bounced around. This represents binary information, 0 and 1.
The resulting change of the resistance is the key principle for spintronic devices, whose magnetic state, which can be considered as stored information, is maintained indefinitely.
Just as a fridge magnet does not need power to remain stuck to the door, spintronic devices would require much less power than conventional electronics.
However, akin to taking a fish out of water, spin information is quickly lost and cannot travel far when electrons are taken out of the ferromagnet.
This major limitation can be overcome by utilizing light through its circular polarization, also known as helicity, as another spin carrier.
Just as humans centuries ago used carrier pigeons to transport written communication farther and faster than could be done on foot, the trick would be to transfer electron spin to photos, the quantum of light.
The presence of spin-orbit coupling, which is also responsible for the spin information loss outside of the ferromagnet, makes such transfer possible.
The crucial missing link is then to electrically modulate the magnetization and thereby change the helicity of the emitted light.
“The concept of spin-LEDs was initially proposed at the end of the last century,” Dr. Lu said.
“However, for the transition into a practical application, it must meet three crucial criteria: operation at room temperature, no need of magnetic field, and the ability for electrical control.”
“After more than 15 years of dedicated work in this field, our collaborative team has successfully conquered all obstacles.”
In their research, Dr. Lu and colleagues successfully switched the magnetization of a spin injector by an electrical pulse using the spin-orbit torque.
The electron’s spin is rapidly converted into information contained in the helicity of the emitted photons, enabling a seamless integration of magnetization dynamics with photonic technologies.
This electrically controlled spin-photon conversion is now achieved in the electroluminescence of light-emitting diodes.
In the future, through the implementation in semiconductor laser diodes, so-called spin-lasers, this highly-efficient information encoding could pave the way for rapid communication over interplanetary distances since polarization of light can be conserved in space propagation, potentially making it the fastest mode of communication between Earth and Mars.
It will also greatly benefit the development of various advanced technologies on Earth, such as optical quantum communication and computation, neuromorphic computing for artificial intelligence, ultrafast and highly-efficient optical transmitters for data centers or Light-Fidelity applications.
“The realization of spin-orbit-torque spin injectors is a decisive step that will greatly advance the development of ultrafast and energy-efficient spin-lasers for the next generation of optical communication and quantum technologies,” said Ruhr University’s Professor Nils Gerhardt.
The team’s work was published in the journal Nature.
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P.A. Dainone et al. 2024. Controlling the helicity of light by electrical magnetization switching. Nature 627, 783-788; doi: 10.1038/s41586-024-07125-5
Source : Breaking Science News