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Here’s what you’ll learn when you read this story:

  • For 150 years, scientists and engineers have leveraged the Hall effect in a variety of applications, both consumer and scientific.

  • Now a new study has found a curious new form of the Hall effect, known as the transdimensional anomalous Hall effect, or TDAHE.

  • Using a specific array of ultra-thin carbon atoms, scientists discovered that electrons in the material exhibited 3D behavior even though its thinness should have precluded such a possibility.

On a fall day in 1879, while working in Johns Hopkins University’s physics lab on his doctoral thesis, 23-year-old American physicist Edwin Hall made an incredible discovery. Hall inserted a small strip of gold foil carrying an electric current between two electromagnets facing each other and discovered that the magnetic field had effectively pushed the electric current toward one side of the strip.

According to Johns Hopkins University, Hall also observed a voltage perpendicular to both the magnetic field and the applied current. This discovery eventually became known as the Hall effect (and its potential difference across the electrical conductor was named Hall voltage)—not bad for a 23-year-old.

In the nearly 150 years since, scientists have discovered a variety of different Hall effects, including the quantum Hall effect, spin Hall effect, and anomalous Hall effect (AHE). Meanwhile, engineers have leveraged the phenomenon to build ion thrusters, while astrophysicists have pondered if the effect played a role in the formation of stars throughout the universe. Now, in a new study published in the journal Nature, an international team of scientists led by experts at Nanjing University in China have discovered a new kind of Hall effect known as a “transdimensional anomalous Hall effect,” or TDAHE.

Anomalous Hall effects arise when ferromagnetic materials exhibit a Hall-like behavior driven by their own internal magnetization, without the need for an externally applied magnetic field. Hall himself discovered this phenomenon two years after his initial discovery of the ordinary Hall effect.

According to New Scientist, the team, led by Lei Wang at Nanjing University, arranged a thin material of carbon atoms in a pattern of rhombuses. The idea was to form “perfectly efficient currents,” but the embedded electrons had other plans.

“TDAHE came about as a complete surprise, a phenomenon never seen in any other material before, nor does any theory predict that,” Wang told New Scientist. “After we measured the raw data, we spent about one year [trying] to understand it.”

This unexpected discovery involved two different-yet-perpendicular electric fields, which caused the 2D material’s electrons to form both horizontal and vertical looping motions, something thought to be impossible due to the material’s incredible thinness at around two to five nanometers. According to New Scientist, the scientists first thought it was just an error but eventually had to come to the conclusion that the electrons were doing something never seen before.

Wang stresses that this isn’t a bridge between 2D and 3D realms and instead wants to stress that this is an entirely new regime for exploration.

“Our observation of the giant in-plane orbital magnetization is unexpected,” the authors write. “Although previous theoretical studies have explored potential mechanisms for realizing in-plane magnetization AHE/QAHE [quantum anomalous Hall effects] in strongly spin–orbit-coupled materials, the experimental realization remains highly challenging.”

Some 150 years later, and there’s still more to learn.

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