New superconductor technology carries data beyond zeros and ones

DURHAM, NC — Remember flip phones? Our smartphones may one day seem just as obsolete thanks to spintronics, a nascent field of research that promises to revolutionize the way our electronic devices send and receive signals.

In most current technologies, data is encoded as zero or one, depending on how many electrons hit a capacitor. With spintronics, data is also transferred depending on the direction of rotation of these electrons.

In a new study published this week in the Proceedings of the National Academy of Sciences, a team of Duke University and Weizmann Institute researchers led by Duke chemistry professor Michael Therien reports an achievement key in the field: the development of a system that controls electron spin and transmits spin current over long distances, without the need for the ultra-cold temperatures required by typical spin conductors.

“The structures we present here are exciting because they define new strategies for generating large-amplitude spin currents at room temperature,” said Chih-Hung Ko, first author of the paper and recent Duke chemistry PhD.

Electrons are like spinning tops. Spin-up electrons spin clockwise and spin-down electrons spin counter-clockwise. Electrons of opposite spins can occupy the same volume, but electrons spinning in the same direction repel each other, like magnets of the same polarity.

By controlling how electrons spin along a current, scientists can encode a new layer of information into an electrical signal.

Rather than just turning capacitors on and off in a binary fashion, spintronic devices could also send signals based on the spin of the electron, where spin-up can mean something different than spin-down.

“Because spin can be up or down, it’s binary information that isn’t harvested in conventional electronic devices,” said David Beratan, professor of chemistry and physics at Duke and co-author of the article.

Ordinary device currents are composed of an equal number of spin-up and spin-down electrons. At room temperature, it is difficult to generate a current composed largely of a single spin. The turns overturn, collapse on top of each other, fall apart and distort the signal like a bad telephone game.

Now Therien and his team have developed a strategy to build molecular conductors that keep electrons in line, ensuring they all spin in harmony and propagate spin direction over long distances, allowing signals to be transmitted. with high fidelity, at room temperature.

“It all depends on the persistence of this spin polarization,” Beratan said. “These spins get jostled around, they interact with surrounding molecules, with anything that might be nearby, and that can knock them over. Here, their spin orientation persists, over long durations and long distances. They stay online.

Electrons spinning in the wrong direction can be filtered out of a system using a special class of molecules called chiral molecules.

Chiral molecules are molecules that are distinguished by their laterality. Like our right and left hands, these molecules are mirror images of each other. They can be left-handed or right-handed, and their laterality serves as a filter for the spins of the electrons. Just as you would be ejected from a treadmill if you stopped walking in the right direction, electrons spinning in a direction opposite to that of the molecule are filtered out.

Thérien and his team had previously developed structures called molecular threads – molecules strung together like threads, which can very easily spread electrical charges. In this new study, the team manipulated these molecular wires and added chiral elements, obtaining a system that not only transmits charges with very low resistance, but also transmits charges with the same spin, by forcing all the electrons to spin the same way.

“We have integrated charge propagation and spin polarization functions into the same molecular wire for the first time,” Therien said.

Ron Naaman, a professor at the Weizmann Institute whose lab has built devices based on Therien molecules, said the spin-selective transport enabled by these systems holds enormous potential for encoding and transmitting information.

The fact that these molecular wires transmit spins at room temperature makes them promising for the development of new technologies.

“Selectively transmitting spin at room temperature over long distances without phase shift opens opportunities for a wider range of devices and may be important for quantum information science,” Therien said.

“Having to cool your computer with liquid nitrogen wouldn’t be very practical,” Beratan said. “If we could deal with spins efficiently at room temperature, that would really be a breakthrough in their practical application.”

Funding for this study was provided by the Center for Synthesizing Quantum Coherence (CHE-1925690), BSF-NSF (2015689), and the Minerva Foundation. CH.K. received a scholarship from the Graduate Program in Nanoscience at Duke University. GB received a John T. Chambers Scholars Award from the Fitzpatrick Institute of Photonics at Duke University. MJT received a John Simon Guggenheim Memorial Foundation Fellowship.

QUOTE: “Twisted molecular wires polarize spin currents at room temperature», Chih-Hung Ko, Qirong Zhu, Francesco Tassinari, George Bullard, Peng Zhang, David N. Beratan, Ron Naaman, Michael J. Therien. Proceedings of the National Academy of Sciences, February 4, 2022. DOI: https://doi.org/10.1073/pnas.2116180119

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