Researchers from George Mason University, National Institute for Materials Science in Tsukuba, Japan, National Institute of Standards and Technology and Brown University have developed a method based on thermopower to detect fractional quantum Hall states of matter.
Fractional quantum hall (FQH) effect is a rare state of matter that could lead to the development of topological quantum computers, which are believed to be more stable against errors than current quantum computers. Plus, FQH may also facilitate the creation of new quantum materials and applications. However, detecting and studying FQH in detail has been very challenging using the existing methods, which involve measuring a material’s ability to resist electric current flow. In this recent work, the team addressed this challenge using an entirely different approach. Instead of relying on electrical resistivity, the researchers tried a different method based on thermopower — a property where a material generates a small voltage when it is heated in a way that its one side is hot, and the other remains cool.
The heat causes the electrons to move from the hot region to the cooler region, creating a voltage. “It turns out that by measuring this voltage (i.e., thermopower), one can measure the entropy of the system, a thermodynamic quantity,” Fereshte Ghahari, one of the researchers and a professor of physics at George Mason Univesity (GMU), said.
Previous studies suggest that thermopower and entropy are directly proportional to each other, and they are closely linked to the unusual quantum behavior of FQH state. Therefore, thermopower measurements provide deeper insights into these exotic states than resistivity measurements alone. The team decided to test this phenomenon.
They picked Bernal-stacked bilayer graphene, a material in which graphene atoms in one layer align partially with the atoms in the second layer, forming a unique structure. This special stacking affects the way electrons move through the material, making it an excellent platform for studying quantum effects like the FQH states.
When the scientists heated the material and performed thermopower measurement, they could detect FQH states like never before. The thermopower signals revealed FQH states with exceptional sensitivity.
Such findings wouldn’t have been possible using the traditional resistivity approach. “We demonstrate that the magneto-thermopower detection of fractional quantum Hall states is more sensitive than resistivity measurements,” the researchers note. “Overall, our findings reveal the unique capabilities of thermopower measurements, introducing a new platform for experimental and theoretical investigations of correlated and topological states in graphene systems, including moiré materials,” Ghahari concluded.
Hopefully, these findings will help realize the true potential of the FQH effect. However, whether the same approach could be used to detect other exotic quantum states remains to be explored through further research.
