Scientists Discover Chiral Crystals Exhibiting Exotic Quantum Effects

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They studied the atoms’ arrangement on the surface of the material using several techniques, such as checking for the right kind of symmetry using the scanning tunneling microscope in Hasan’s Laboratory for Topological Quantum Matter and Advanced Spectroscopy located in the basement of Princeton’s Jadwin Hall.

The chiral crystals were then taken to Lawrence Berkeley National Laboratory, where members of the research team used high energy X-rays to knock electrons off the surface, as analyzing the patterns made by the emitted electrons can reveal their masses and velocities. The researchers found that electrons emitted from deeper within the samples had effectively zero mass, and their velocity and spin distributions revealed both their chiral (handed) behavior and their collective monopole-like character.

“It is amazing to see that somehow the chirality of the crystal structure has a profound effect on the electrons in these materials — they are now massless and chiral,” said Tyler Cochran, a physics graduate student and one of the three co-first authors of the paper.

“We expect this is the tip of the iceberg,” said fellow graduate student and co-first author Ilya Belopolski. “There are so many chiral crystals in nature. It would be great to check how many of those are topological. This would be a fantastic playground for new types of quantum phenomena.”

“Chiral crystals seem to be a perfect source for novel electronic phases of matter and more excitingly, for the massless electrons of the kind physicists were searching for many years,” said Daniel Sanchez, another co-first author. “This is just terrific that we found them.”

The researchers were excited to discover this quantum-level chiral behavior of electrons, said Guoqing Chang, a postdoctoral research associate in Hasan’s lab who was the first author of the theory paper predicting these topological phenomena. “It is one of those examples where our theoretical predictions have been realized experimentally,” he said. “That does not always happen. We predicted something new that agreed with what Mother Nature had in store for us — this is just exciting.”

 “It is indeed immensely satisfying when you predict something exotic and it also appears in the laboratory experiments,” Hasan said. “This is not the first time we have succeeded in predicting topological effects in quantum physics. We successfully predicted some of the new bismuth-based topological insulators that are now among the mostly studied compounds in the field.”

He added, “We are combining theory and experiments to advance the knowledge frontier.”

The team included numerous researchers from Princeton’s Department of Physics, including present and past graduate students Daniel Sanchez, Ilya Belopolski, Tyler Cochran, Nasser Alidoust, Daniel Multer, Songtian Sonia Zhang, Nana Shumiya and Suyang Xu, and present and past postdoctoral research associates Jia-Xin Yin, Guoqing Chang and Weiwei Xie. Other co-authors were Xitong Xu, Kaustuv Manna, Vicky Süß, Cheng-Yi Huang, Xirui Wang, Guang-Qiang Wang, Tay-Rong Chang, Claudia Felser, Shuang Jia and Hsin Lin.

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