Chiral Phonons in Quantum Materials
Location: CECAM-Lugano, Aula Magna, USI West campus, Lugano, Switzerland
Angular momentum coupling lies at the heart of many fundamental physical phenomena. For example, the spin-orbit interaction, which couples the spin and orbital angular momenta of electrons or nuclei, famously leads to the fine and hyperfine splittings of electronic energy levels in atoms. In solids, the breaking of time-reversal symmetry by electronic angular momentum enables complex magnetic and topological orders exhibiting various Hall effects, as well as chiral phases ranging from chiral spin liquids to chiral superconductors. At the same time, the angular momentum of light is a well-established quantity, which can interact with the electrons and nuclei to either distinguish or induce chirality in atomic, molecular, and solid-state systems.
Over the last few years, a rapidly increasing amount of research has focused on the angular momentum generated by vibrations of the crystal lattice (phonons) in solids. Phonon angular momentum is made up by circular or elliptical orbital motions of the atoms around their equilibrium lattice positions and the resulting collective vibrational pattern is called a chiral phonon mode [1, 2]. The existence of chiral phonons and phonon angular momentum leads to a rich variety of novel collective phenomena, where recent examples from theoretical, computational, and experimental work include the phonon Hall [3, 4], phonon Einstein-de Haas [5, 6], phonon Faraday [7, 8], and phonon Zeeman effects [8, 9].
So far, research on chiral phonons and phonon angular momentum has evolved in parallel within different areas of condensed matter physics and materials science, including, most prominently, the spintronics community, the two-dimensional (2D) optoelectronics community, the ultrafast dynamics community, and the thermal transport community. Although the underlying physical mechanisms are all associated with phonon angular momentum, there has been surprisingly little cross-interaction between the different fields. The methodologies and materials systems have mostly been orthogonal, and even the definitions of chiral phonons vary. In this workshop, we aim to bring members from these different communities together in order to discuss the phenomena arising from chiral phonons across fields under the overarching principle of phonon angular momentum coupling. We believe that discussing chiral phonon physics within a unified workshop will strengthen interdisciplinary research efforts and enable cross-investigations of fundamental questions related to angular momentum in solids.
In particular, we aim to bring members from the following communities and working on following specific topics together:
1) Magnetism and spintronics: Spin-phonon coupling and interactions of chiral phonons with magnetic fields, phonon magnetic moments, Zeeman and Faraday effects of chiral phonons, chiral phonon-mediated exchange, and spin relaxation.
2) 2D optoelectronics: Electron- and exciton-phonon coupling of chiral phonons in layered and 2D materials, chiral phonons in Moiré lattices, and phonon angular momentum coupling to topological electronic band structures.
3) Ultrafast dynamics: Coherent excitation of chiral phonons with ultrashort laser pulses, dynamical time reversal symmetry breaking, dynamical multiferroicity, generation of effective magnetic fields, and ultrafast control of magnetic order.
4) Transport and Hall effects: Contributions of chiral phonons to thermal transport and expansion, thermal Hall effects based on phonon angular momentum, chiral phonons in cuprate superconductors.
Dominik Juraschek (Tel Aviv University) - Organiser & speaker
Matthias Geilhufe (Chalmers University of Technology) - Organiser & speaker
Hanyu Zhu (Rice University) - Organiser & speaker