An old physical phenomenon, known as the Hall effect, has revealed some new tricks, according to a team co-led by researchers at Penn State and the Massachusetts Institute of Technology (MIT). They reported their findings, which they said have potential implications for understanding fundamental physics of quantum materials and developing applied technologies such as quantum communication and harvesting energy via radio frequencies, this week (Oct. 21) in Nature Materials.
The conventional Hall effect occurs only in electrical conductors or semiconductors in the presence of a magnetic field. It is characterized by a newly formed voltage, called the Hall voltage, that can be measured perpendicularly to the current and is directly proportional to the applied current.
However, the newly discovered nonreciprocal Hall effect does not require a magnetic field. Discovered by teams led by Zhiqiang Mao, professor of physics, of materials science and engineering and of chemistry at Penn State, and Liang Fu, professor of physics at MIT, this effect is instead denoted by a relationship between the Hall voltage and the applied current that can be described mathematically: The Hall voltage is always proportional to the square of the current. They made the finding in microstructures comprising textured platinum nanoparticles deposited on silicon.
Unlike the conventional Hall effect, which is driven by a force induced by the magnetic field, the nonreciprocal Hall effect arises from flowing conduction electrons — which are particles that carry the electrical charge — interacting with the textured platinum nanoparticles.
“In this work, we report the first observation of a room-temperature colossal nonreciprocal Hall effect,” Mao said, explaining that pronounced geometric asymmetric scatterings of the textured platinum nanoparticles enabled the observation. “We also showcased the potential application of this effect for broadband frequency mixing and wireless microwave detection. This underscores the vast potential of utilizing nonreciprocal Hall devices for terahertz communication, imaging and energy harvesting.”
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