A Century-Old Physics Effect Gains a New Dimension

Challenging a Century-Old Physics Assumption About the Hall Effect

Edwin Hall discovered in 1879 that applying a magnetic field perpendicular to an electric current deflects moving charges to create a measurable voltage. According to Carnegie Mellon University physics professor Simranjeet Singh, scientists operated for generations under the assumption that this phenomenon exclusively required a perpendicular magnetic field. Working in the university’s Lab for Investigating Quantum Materials, Interfaces and Devices (LIQUID), the research team proved that materials can also yield a measurable response when the magnetic field is positioned in-plane. This expanded understanding gives physicists a new tool to probe complex magnetic and topological structures in condensed matter systems.

Building Atomically Precise Heterostructures for Multidimensional Sensing

While theoretical physicists had previously suggested an in-plane anomalous Hall response might exist, experimental verification remained elusive because finding a material with the correct crystalline symmetry and magnetic properties was exceedingly difficult. To overcome this hurdle, Singh collaborated with fellow Carnegie Mellon physics professor Jyoti Katoch, who specializes in fabricating devices from two-dimensional quantum materials alongside postdoctoral researchers I-Hsuan Kao and Ravi Kumar. The team utilized tantalum iridium telluride (TaIrTe4), a material possessing the precise symmetry required for a multidimensional Hall effect. Researchers reduced the material to just a few atomic layers and placed it directly adjacent to a magnetic layer called Cr2Ge2Te6 (CGT).

Because the two materials sit in such close proximity, magnetism from the CGT layer influences the normally nonmagnetic TaIrTe4. This grants the TaIrTe4 magnetic properties while preserving its core electronic behavior. “This truly demonstrates the power of building atomically precise heterostructures of emergent two-dimensional quantum materials to obtain on-demand electronic and magnetic properties,” Katoch said.

How Spin-Orbit Coupling Enables Single-Device Vector Magnetometry

To explain the underlying physics of the unconventional response, assistant professor of physics Shubhayu Chatterjee performed theoretical modeling. Chatterjee found that pairing TaIrTe4 with CGT reduces the symmetry of the combined system, which in turn generates additional spin-orbit coupling at the interface once the CGT becomes ferromagnetic at low temperatures. This interaction between an electron’s motion and its quantum spin is critical for creating the in-plane anomalous Hall effect. Inside these atomically thin devices, the team detected both the conventional Hall signal and a second signal tied to in-plane magnetization. “You can do multidimensional magnetic sensing with one sensor only,” Singh noted, explaining that engineers previously needed to deploy two separate sensors to measure magnetic fields across multiple directions.

Hall Effect Type	Field Orientation	Technological Impact
Conventional Hall Effect	Perpendicular to plane	Standard sensing in cars and keyboards
In-Plane Anomalous Hall Effect	Parallel to plane (In-plane)	Multidirectional sensing with a single device

Next Steps for Practical Magnetic Sensors

The LIQUID team is actively investigating other material combinations that could replicate this unconventional Hall behavior. Researchers are also testing how the microscopic devices perform at room temperature, a vital benchmark for turning the phenomenon into commercially viable sensing technology. As the team refines these atomically thin architectures, the potential to simplify planar device designs and streamline vector magnetometry moves closer to real-world deployment.

Frequently Asked Questions

What is the Hall effect?

Discovered by Edwin Hall in 1879, the Hall effect occurs when a magnetic field applied perpendicular to an electric current deflects moving charges, generating a measurable voltage that reveals key material properties.

What did Carnegie Mellon researchers discover?

Researchers identified an in-plane anomalous Hall effect, demonstrating that electronic materials can produce a magnetization-dependent Hall response when the magnetic field is parallel to the material’s plane.

Why is this discovery important for future technology?

By detecting magnetic fields along multiple axes within a single ultrathin device, the finding could enable simpler, more flexible vector magnetometers and sensors for electronics, transportation, and medical imaging.