Electron paths can enhance the magnetism of collective atomic vibrations

Materials with enhanced thermal conductivity are critical to the development of advanced devices that support communications, clean energy, and aerospace applications. But in order to design materials with such properties, scientists need to understand how phonons, or quantum units of atomic vibrations, behave in specific materials.

“Phonons are important for studying new materials because they control a variety of material properties, such as thermal conductivity and carrier properties,” said Fuyang Tay, a graduate student in applied physics who is studying the Rice Advanced Magnets and Broadband Optics (RAMBO) ) tabletop spectrometer in Junichiro Kono’s laboratory at Rice University. “For example, it is widely believed that superconductivity arises from electron-phonon interactions.

“Recently, there has been increasing interest in the magnetic moments carried by phonon patterns that exhibit circular motion, also known as chiral phonons. But the mechanisms that lead to the magnetic moments of large large phonons are not yet understood.”

Now, an international team of researchers led by Felix Hernandez of the University of São Paulo in Brazil and Andrey Baydin, an assistant research professor at Rice University, has published a study detailing the underlying topology of these quantum spinning dervishes’ magnetism and the material’s electronic band structure. complex connections between. , which determines the energy level range of electrons.

This discovery enriches the body of knowledge about phonons and opens the door not only to more efficient manipulation of phonons through magnetic fields, but also to the development of advanced materials.

In previous research, Baydin and colleagues applied magnetic fields to lead telluride, a simple semiconductor material. When they did this, they found that the phonons stopped vibrating in a linear manner and became chiral, moving in a circular motion.

“Chiral phonons interact differently than phonons that move linearly,” Bedin said. “If we understand the properties of these interactions, we can exploit them. Different properties enable different potential applications in the material.”

After noticing that the magnetic moments of chiral phonons in the materials they first focused on were very small, the team wondered whether changing the topology or electronic band structure of the materials would affect magnetism. To answer this question, researchers tested a new material called a crystalline topological insulator.

“We took lead telluride and added tin to it,” Bedin said. “If you add enough, a band inversion occurs, resulting in topologically protected surface states. These materials are interesting because they are insulating in bulk but have conducting electronic surface states, which is a very promising properties that can be exploited in new electronic devices.”

Additional experiments showed that the magnetic moments of chiral phonons in topological materials are two orders of magnitude larger than in materials without this electronic topology.

“Our results reveal compelling new insights into the magnetism of phonons in this material and highlight the complex connection between the magnetism of chiral phonons and the underlying electronic band structure topology of the material,” Beding said. He added that the group plans to conduct further experiments in the future to better understand other aspects of phonon behavior.

Tay added that these results show that the phonon magnetic moment is significantly enhanced in topological materials and can help materials scientists search and design materials with larger phonon magnetic moments according to the needs of different device applications.

“This observation provides new insights into how phonon properties can be controlled and manipulated to change thermal conductivity,” Tai said. “Furthermore, the interaction between chiral phonons and electronic structure topology raises the question of how to control phonons by controlling phonon properties.” to influence the topological phase.”