Physicists discover a quantum state with a new type of emerging particle: six-stream composite fermions

If the fractional quantum Hall regime were a series of highways, these highways would have two or four lanes. The flow of two- or four-stream composite fermions, like that of automobiles in this two- or four-stream composite fermion traffic scenario, naturally explains the more than 90 fractional quantum Hall states that form in a wide variety of host materials . However, physicists at Purdue University recently discovered that fractional quantum Hall regimes are not limited to two or four streams and discovered the existence of a new type of emerging particle, which they call composite fermion at six streams.

They recently published their groundbreaking findings in Natural communications.

Gabor Csathy, professor and head of the Department of Physics and Astronomy at Purdue University College of Science, as well as a Ph.D. students Haoyun Huang, Waseem Hussain and recent Ph.D. Graduate Sean Myers led this discovery from Purdue’s West Lafayette campus. Csathy credits lead author Huang with designing and directing the measurements and writing much of the manuscript. All very low temperature measurements were carried out in the laboratory of the Csathy physics building. His laboratory conducts research in highly correlated electronic physics, sometimes called topological electronic physics.

The weak interactions of electrons are well established and their behavior is entirely predictable. When electrons interact weakly, the electron is generally considered the natural building block of the entire system. But when electrons interact strongly, it becomes almost impossible to interpret systemic behavior by thinking about individual electrons.

“This happens in very few cases, like in the fractional quantum Hall regime that we study, for example,” says Csathy. “To explain fractional quantum Hall states, the composite fermion, a very intuitive fundamental element, comes in different flavors. They can explain a whole subset of fractional quantum Hall states. But all fully expanded states (i.e. i.e. topologically protected), fractional quantum Hall states could be explained by only two types of composite fermions: two-stream and four-stream composite fermions.

“We have reported here a new fractional quantum Hall state that cannot be explained by any of these previous ideas. Instead, we must invoke the existence of a new type of emerging particle, six-stream composite fermions The discovery of new fractional quantum Hall states is quite rare. However, the discovery of a new emerging particle in condensed matter physics is truly rare and astonishing.

For now, these ideas will be used to expand our understanding of the order of known fractional quantum Hall states in a “periodic table.” Particularly notable in this process is that the emerging composite fermion particle is unique in that the electron captures six quantized magnetic flux quanta, forming the most complex composite fermion known to date.

“The numerology of this complex physical puzzle requires some patience,” says Haoyun Huang, Csathy’s Ph.D. student. “Let’s take the example of the fractional state nu=2/3. Since 2/3=2/(2*2-1), the nu=2/3 state belongs to the family of two flows. Similarly, for the fractional state nu=2/7, 2/7=2/(2*4-1), this state therefore belongs to the family of four flows. In contrast, the fractional states we discovered are closely related to 2/11=2/(2*6-1). Prior to our work, no fully quantized fractional quantum Hall state had been observed that could be associated with six-stream composite fermions. The situation was completely different theoretically: the existence of these types of composite fermions was predicted by Jainendra Jain in his highly influential theory of composite fermions published in 1989. The associated quantization was not observed during these 34 years. »

The material used in this study was grown by a Princeton University team led by Loren Pfeiffer. The electrical quality of the GaAs semiconductor played a major role in the success of this research. According to Csathy, this Princeton group is the world leader in producing the highest quality GaAs-based materials.

“The GaAs they grow is very special, because the number of imperfections is surprisingly low,” he says. “The combination of low disorder and the very low temperature measurement expertise of the Csathy lab made this project possible. One of the reasons we were measuring these samples is that very recently the Princeton group has significantly improved the quality of the GaAs semiconductor, as measured by the tiny amounts of defects present. These improved samples will, for sure, continue to provide a playground for new physics.

This exciting discovery is part of ongoing research by Csathy’s team. The team continues to push the boundaries of discovery in its persistent quest for topological electronic physics.