The Hall effect, a long-known physical phenomenon, has uncovered new insights recently. Research led by teams from Penn State and the Massachusetts Institute of Technology (MIT) suggests that these findings could have significant effects on our understanding of quantum materials and could inform technologies like quantum communication and energy harvesting using radio frequencies.
The Hall effect, an established physical phenomenon, has shown some fresh developments, as noted by a research team co-directed by scholars at Penn State and MIT. Their findings, reported on October 21 in Nature Materials, may influence how we comprehend the basic physics of quantum materials and facilitate advancements in applied technologies, such as quantum communication and energy capture through radio frequencies.
The traditional Hall effect is observed in electrical conductors or semiconductors when a magnetic field is present. It produces a Hall voltage that can be measured perpendicular to the direction of the electric current and is directly related to the applied current.
In contrast, a newly identified nonreciprocal Hall effect operates without needing a magnetic field. This phenomenon, discovered by teams led by Penn State’s Professor Zhiqiang Mao and MIT’s Professor Liang Fu, features a mathematical relationship where the Hall voltage scales with the square of the applied current. They made this discovery using microstructures with textured platinum nanoparticles on silicon.
Unlike the conventional Hall effect, which relies on forces from the magnetic field, the nonreciprocal Hall effect stems from the interplay between flowing conduction electrons—charged particles—and the textured platinum nanoparticles.
“We have recorded the first instance of a room-temperature colossal nonreciprocal Hall effect,” Mao explained, attributing this to the marked asymmetrical geometric scattering of the textured platinum nanoparticles. “Additionally, we demonstrated the potential for this effect in applications such as broadband frequency mixing and wireless microwave detection, showcasing its great promise for terahertz communication, imaging, and energy harvesting.”
This work is rooted in understanding electron scattering patterns when electrons interact with asymmetrical particles. This leads to a breach of Ohm’s law—formulated by physicist Georg Ohm in 1827—which posits that the current in a conductor is proportional to the applied voltage, predicting that Hall voltage should be zero without a magnetic field. However, the nonreciprocal Hall voltage display observed with textured platinum nanoparticles at zero magnetic field contradicts this principle.
Mao emphasized that the findings are particularly noteworthy because investigations into such behaviors usually require low temperatures, below 280 degrees Fahrenheit. In this case, the irregular structure of the deposited platinum nanoparticles facilitates the nonreciprocal Hall effect even at room temperature. This discovery could advance technologies in areas such as quantum rectification (the process of converting alternating currents to direct current) and photodetection (generating electrical signals from light), according to Mao.
“This achievement enhances our grasp of charge movement in materials,” Mao stated, underscoring that asymmetric electron scattering is vital for the nonreciprocal Hall effect in the textured platinum nanoparticles. “This asymmetry uncovers uneven features where uniformity would generally exist, and these regions may lead to significant new findings.”
Co-authors from Penn State include Lujin Min, formerly a doctoral student in materials science and engineering and now a postdoctoral associate at Cornell University; Seng Huat Lee, an assistant research professor in the Materials Research Institute (MRI); Yu Wang, a research technician with MRI’s 2D Crystal Consortium; Sai Venkata Gayathri Ayyagari, a graduate student in materials science and engineering; Leixin Miao, previously a doctoral student and now a yield development engineer at Intel, and Nasim Alem, an associate professor of materials science and engineering. Collaborators from MIT include Yang Zhang, Yugo Onishi, Liang Fu, and Zhijian Xie from North Carolina Agricultural and Technical State University.
This research was backed by support from Penn State, the U.S. National Science Foundation, U.S. Army Research Laboratory, U.S. Army Research Office through the Institute for Soldier Nanotechnologies, the David and Lucile Packard Foundation, and the Funai Overseas Scholarship.
