Phonon Berry Curvature in Quantum Materials
Abstract
Phonons are the quantum mechanical vibrations of a solid material. Phonons determine many material properties, including how well ceramics insulate from heat, and how easily electrons move through a metal. It is surprising, then, that something so fundamental to our understanding of material science can continue to present experimental mysteries. One recently-discovered mystery is that, in some materials, phonons carrying heat can be deflected to the left or to the right by applying a magnetic field. This effect, known as thermal Hall effect, is well-understood for electrons because electrons carry electrical charge and interact with magnetic fields through well-understood laws of physics. Phonons, on the other hand, have no electric charge, thus the appearance of a phonon Hall effect is a great puzzle. The materials where the phonon Hall effect occurs include high-temperature superconductors and so-called spin liquids that are being studied for their applications to quantum computing. Given the central importance of superconductors and spin liquids, it is critical that we understand where the phonon thermal Hall effect is coming from. This research will use ultrasound to study why phonons in these materials are behaving so strangely. Ultrasound is a controlled way of generating phonons that all have the same period of vibration, sort of like a phonon laser . Using ultrasound, we can precisely measure if phonons rotate their orientation, the direction they vibrate, as they travel through a material when we turn on a magnetic field. This can happen because of something called Berry curvature , which is closely analogous to the curvature that space-time experiences due to gravity. Phonon Berry curvature is a possible explanation for the phonon thermal Hall effect but it has never been observed. If we find it, we will answer several outstanding questions in the field of quantum materials.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 29, 2024
- Source ID
- FA95502310306
Entities
People
- Brad Ramshaw
Organizations
- Air Force Office of Scientific Research
- Cornell University
- United States Air Force