A very large occurrence of a long-studied phenomenon related to electromagnetism has been recorded by scientists in Japan, according to newly published research.
The findings, made by a team at the Institute of Science in Tokyo, Japan, involve the anomalous Hall effect, a phenomenon that occurs in solid materials where broken time-reversal symmetry results from spin-orbit coupling.
The Tokyo scientists made the surprising discovery using thin films made of high-quality cadmium arsenide beneath an in-plane magnetic field, according to a study published in the journal Physical Review Letters, which they say produced a much larger anomalous Hall effect than previously recorded by researchers.
The Anomalous Hall Effect
Initially discovered in 1879 by American physicist Edwin Hall, the phenomenon known as the Hall effect arises from the interaction between a magnetic field and an electric current, resulting in a measurable voltage perpendicular to both. Fundamentally, this phenomenon is caused by the sideways deflection of moving charges.
Following its discovery, several important advancements were made, and over time, it was also discovered that magnetic materials exhibited a similar phenomenon to that observed by Hall, which became known as the anomalous Hall effect (AHE).
As its name would suggest, the anomalous Hall effect is far more perplexing than its counterpart, and scientists remain unsure of what precisely may cause it. Adding to the mystery, some interpretations of its theoretical origins suggest that it may also occur in non-magnetic materials.
In the past, no experimental confirmation of such theories had ever been produced. However, thanks to the efforts of the Tokyo-based team, scientists may now finally have the next pieces to the longstanding puzzle involving the AHE.
A Nonmagnetic AHE Observation
In the team’s new study, led by Associate Professor Masaki Uchida from the Institute of Science, Tokyo, Japan, what is believed to be the first observation of the AHE in a nonmagnetic material was achieved using films of cadmium arsenide, a variety of Dirac semimetals.
Such materials possess special features known as Dirac points, where electrons behave in a unique way that exhibits the qualities of massless particles. However, when subjected to the effects of very strong magnetic fields, these Dirac points undergo transformations due to symmetry breaking, which causes even stranger electron behavior.
Based on these unique qualities, Uchida and the Tokyo team were able to modulate the properties of the cadmium arsenide films, allowing them to limit the effects of the normal Hall effect and capture data solely related to the effects of the AHE.
A Phenomenon of Giant Proportions
Applying in-plane magnetic fields to the arsenic cadmium material, measurements of the changes in conductivity allowed the team to gauge the size of the anomalous Hall effect, with a surprising result: they were able to successfully generate a “giant” AHE during their experiments.
“The approach used in our study is widely applicable beyond Dirac semimetals,” the team said in a statement, adding that their findings potentially challenge existing ideas about Hall effects.
“Future research could lead to the development of next-generation devices,” Uchida said of their discovery. Fundamentally, the team’s findings regarding the AHE help offer pathways toward new research studies that can examine the unique properties of electrons based on orbital magnetization.
Breaking New Ground
“Our study is the first to experimentally confirm that AHE can be quantitatively detected in nonmagnetic materials using in-plane magnetic fields,” Uchida said, adding that he expects the team’s findings will soon help facilitate new discoveries and applications, much like the initial discovery of the Hall effect did more than a century and a half ago.
“Hall sensors and other devices that exploit AHE in nonmagnetic materials could become more efficient,” Uchida adds, “and operate under broader conditions than current technologies.”
The team’s new paper, “Anomalous Hall effect in the Dirac semimetal [cadmium arsenide] probed by in-plane magnetic field,” appeared in Physical Review Letters.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.