Physicists discover a quantum state with a new type of emergent particles: Six-flux composite fermions

If the Fractional Quantum Hall system were a series of highways, these highways would have either two or four lanes. A two-flux or four-flux composite fermion flow, such as an automobile in this two- to four-flux composite fermion traffic scenario, naturally describes more than 90 fractional quantum Hall states that form in a large variety of host materials. . Physicists at Purdue University have recently discovered that fractional quantum Hall regimes are not limited to just two fluxes or four fluxes and have discovered the existence of a new type of emerging particle, which they call a six-flux composite fermion. are

He recently published Their main findings Nature Communications.

With Gaber Sethi, Ph.D., professor and chair of the Department of Physics and Astronomy at Purdue University College of Science. students Hyeon Hwang, Waseem Hussain, and recent Ph.D. Graduate Sean Myers led the discovery from Purdue’s West Lafayette campus. Sethi credits lead author Huang for conceiving and leading the measurements and writing a large portion of the manuscript. All ultra-low temperature measurements were completed in Csathy’s Physics Building lab. His lab conducts research on strongly bound electrons. Physicssometimes called topological electron physics.

The weak interactions of electrons are well established, and the behavior is fairly predictable. While electrons are weakly interacting, the electron is usually considered the natural building block of the whole system. But when electrons interact strongly, it becomes almost impossible to interpret systemic behavior by thinking about individual electrons.

“This happens in very rare cases, like in the fractional quantum Hall systems we study, for example,” says Sethi. “To describe fractional quantum Hall states, composite fermions, a very intuitive basic building block, come in different flavors. They can account for a whole subset of fractional quantum Hall states. But all are fully developed. , (i.e. topologically preserved), fractional quantum Hall states can be accounted for by only two types of composite fermions: two-flux and four-flux composite fermions.

“Here we report a new fractional quantum Hall state that cannot be explained by any of these previous ideas. Instead, we find the existence of a new type of emergent particle, so-called six-flux composite fermions. need to start. New fractional quantum Hall states are quite rare. However, the discovery of a new emerging particle in condensed matter physics is truly rare and surprising.”

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

“Data for this complex physics puzzle requires a lot of patience,” says Haoyun Huang, Csathy’s Ph.D. Students take the nu=2/3 partial condition as an example. Since 2/3=2/(2*2-1), the nu=2/3 state belongs to the two-flow family. Similarly, nu=2/7 for the fractional condition, 2/7=2/(2*4-1), so this state belongs to the four-flow family. In contrast, the partial states we discovered are closely related 2/11=2/(2*6-1). Prior to our work, no fully quantized fractional quantum Hall state that could be associated with a six-flux composite fermion had been observed. On the theory front the situation was quite different: the existence of this type of composite fermion was predicted by Jayendra Jain in his highly influential theory of composite fermions published in 1989. No relevant quantities were observed during these 34 years.”

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

“The way they grow is very special, because the number of defects is surprisingly low,” he says. “The combination of low distortion and ultra-low temperature measurement expertise at the Csathy lab made this project possible. One of the reasons we were measuring these samples is that the Princeton group recently published a new standard for GaAs semiconductors. has been significantly improved, as measured by the small amount of defects present. These improved samples will certainly continue to level the playing field 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 the pursuit of topological electron physics.