Materials with improved thermal conductivity are essential for the development of advanced devices to support communications, clean energy and aerospace applications. But to engineer materials with this property, scientists need to understand how phonons, or quantum units of vibration in atoms, behave in a particular substance.
“Phonons are very important in the study of new materials because they govern many material properties such as thermal conductivity and carrier properties,” said Fuyang Tay, a graduate student in applied physics working with the Rice Advanced Magnet with Broadband Optics (RAMBO), a tabletop spectrometer. in Junichiro Kono’s laboratory at Rice University. “For example, it is widely accepted that superconductivity arises from electronphonon interactions.
“Recently, there has been a growing interest in the magnetic moment brought about by phonon modes that exhibit circular motion, also known as chiral phonons. But the mechanisms that can lead to a large phonon magnetic moment are not well understood.”
Now an international team of researchers led by Felix Hernandez from the Universidade de So Paulo in Brazil and Rice assistant research professor Andrey Baydin has published a study detailing the intricate connection between the magnetic properties of these quantum whirling dervishes. and of a material underlying the topology of the electronic band structure. , which determines the range of energy levels that the electrons in it have.
This finding adds to the growing knowledge of phonons, which opens the door not only for more effective phonon manipulation by magnetic fields, but also for the development of advanced materials.
In a previous study, Baydin and colleagues applied a magnetic field to lead telluride, a simple semiconductor material. When they did this, they found that the phonons stopped vibrating in a linear fashion and became chiral, moving in a circular motion.
“Chiral phonons interact with each other differently than phonons that move linearly,” Baydin said. “If we understand the properties of these interactions, we can use them. Different properties can realize different potential applications of materials.”
After noticing that the magnetic moment of chiral phonons in the material they first focused on was small, the team wondered if changing the material’s topology or electronic band structure would affect the magnetic properties. To answer this question, researchers tested a new material called a crystalline topological insulator.
“We took lead telluride and added tin to it,” Baydin said. “If you add enough, something called band inversion happens, which creates topologically protected surface states. These materials are interesting, because they are largely insulating but conduct the electronic surface states very well feature that can be exploited in novel electronic devices.”
Further experiments revealed that the chiral phonons’magnetic moment is two orders of magnitude greater in the topological material than in the material without such electronic topology.
“Our findings reveal compelling new insights into the magnetic properties of phonons in this material and highlight the intricate connection between the magnetic properties of chiral phonons and the material’s underlying topology electronic band structure,” said Baydin. He added that the team plans to do more experiments to better understand other aspects of phonon behavior in the future.
Tay added that these results, which show that the magnetic moment of phonons is greatly enhanced in topological materials, will help materials scientists to find and design materials with larger phonon magnetic moments when required for various device applications.
“This observation provides new insights into how to control and manipulate phonon properties to change thermal conductivity,” Tay said. “Furthermore, the interplay between chiral phonons and electronic structure topology raises the possibility that the topological phase can be influenced by controlling the phonons.”
Felix GG Hernandez et al, Observing the interplay between phonon chirality and electronic band topology, Advances in Science (2023). DOI: 10.1126/sciadv.adj4074
Provided by Rice University
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