April 13, 2024

Transporting spin information at the speed of light

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SOT rotating LED structure. Credit: Nature (2024). DOI: 10.1038/s41586-024-07125-5

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SOT rotating LED structure. Credit: Nature (2024). DOI: 10.1038/s41586-024-07125-5

Scientists 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 discovery, described in a study published in Natureinvolves the area of ​​spintronics, which aims to manipulate the spin of electrons to store and process information.

The researchers applied an electrical pulse to transfer this spin information from electrons to photons, the particles that make up light, allowing the information to be transported over great distances at great speed. Their method meets three crucial criteria – room temperature operation, no need for a magnetic field, and electrical control capability – and opens the door to a variety of applications, including ultrafast communication and quantum technologies.

“For decades we have dreamed and predicted room-temperature spintronic devices beyond magnetoresistance and just storing information. With this team’s discovery, our dreams come true,” says study co-author Igor Žutić, SUNY Distinguished Professor of Physics at the University. in Buffalo.

The study was led by the Jean Lamour Institute, a joint unit of the French National Center for Scientific Research (CNRS) and the University of Lorraine. Other contributors represent universities and institutes in France, Germany, Japan, China and the United States.

Spintronic devices can replace conventional electronics

In spintronics, which has been used successfully in magnetic computer hard drives, information is represented by the electron’s 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 along or against the axis of magnetization. Electrons with spin along the magnetization travel smoothly through a ferromagnet, while those with opposite spin orientation are bounced. This represents binary information, 0 and 1.

The resulting change in resistance is the key principle for spintronic devices, whose magnetic state, which can be considered as stored information, is maintained indefinitely. Just as a refrigerator magnet does not need energy to remain attached to the door, spintronic devices would require much less energy than conventional electronics.

However, similar to taking a fish out of water, spin information is quickly lost and cannot travel far when electrons are stripped from 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 carry written communications farther and faster than could be done on foot, the trick would be to transfer the spin of electrons to the photographs, the quantum of light.

Spin-LEDs meet three criteria

The presence of spin-orbit coupling, which is also responsible for the loss of spin information outside the ferromagnet, makes such transfer possible. The crucial missing link is then to electrically modulate the magnetization and thus alter the helicity of the emitted light.

“The concept of spin-LEDs was initially proposed at the end of the last century. However, to transition to a practical application, it must meet three crucial criteria: operation at room temperature, no need for a magnetic field, and electrical control capability,” says study corresponding author Yuan Lu, CNRS senior researcher at the Institute Jean Lamour.

“After more than 15 years of dedicated work in this area, our collaborative team has successfully overcome all obstacles.”

The researchers successfully switched the magnetization of a spin injector to an electrical pulse using spin-orbit torque. The electron spin is quickly converted into information contained in the helicity of the emitted photons, allowing 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 implementation in semiconductor laser diodes, so-called spin lasers, this highly efficient information encoding could pave the way for rapid communication across interplanetary distances, since the polarization of light can be conserved in space propagation, making -potentially the fastest mode of communication between Earth and Mars.

It will also greatly benefit the development of various advanced technologies on Earth, such as quantum optical communication and computing, neuromorphic computing for artificial intelligence, ultrafast and highly efficient optical transmitters for data centers or Light-Fidelity (LiFi) 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,” says co-author Nils Gerhardt, Professor at the Chair of Photonics and Terahertz Technology at the Ruhr University in Bochum.

More information:
Pambiang Abel Dainone et al, Controlling the helicity of light by electrical magnetization switching, Nature (2024). DOI: 10.1038/s41586-024-07125-5

Diary information:
Nature

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