A tango between magnons and phonons in 2D van der Waals insulating magnets

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Non-technical:Magnons and phonons, which are quanta of spin waves and lattice vibrations respectively, represent two fundamental collective excitations in condensed matter. In general, magnons and phonons are studied separately. Nevertheless, in magnetic solids with strong spin-lattice interactions, magnon-phonon coupling plays a key role in determining magnetic and thermal properties. Thus far, experimental studies of magnon-phonon coupling in van der Waals magnets, which emerge as a fertile playground for the discovery of novel physical phenomena, remain a largely unexplored research frontier. This project studies the magnon-phonon coupling in van der Waals insulating magnets by utilizing neutron scattering and thermal transport techniques. This project offers an excellent educational experience for young researchers to utilize cutting-edge facilities for scientific research on quantum materials. In addition to training graduate and undergraduate students, this project also supports scientific research activities by engaging K-12 students, attracting underrepresented students to research, and developing workshops. Importantly, this project serves as a platform to train the next-generation of neutron scattering scientists and therefore grows the user community of cutting-edge facilities in national laboratories. Technical:This project studies magnon-phonon coupling in van der Waals insulating magnets to understand the roles of magnons, phonons, and magnon-phonon coupling on thermal transport and thermodynamics of these systems. Specifically, the work addresses the following key scientific questions with neutron scattering and thermal transport techniques: (i) how does the magnon-phonon coupling depend on the symmetry of magnetic ground states? (ii) how does the spin-lattice interaction depend on the electron occupancy on d orbitals of magnetic transition-metal ions, and what is the impact of this on the magnon-phonon coupling? (iii) How does the magnon-phonon coupling vary with the spin-orbit interaction? (iv) How does the magnon-phonon coupling affect materials’ thermal transport and thermodynamics properties? The answers to these questions provide unprecedented knowledge about the coupling between magnons and phonons as well as their impact on thermal properties of van der Waals materials, which are essential for applications of these materials in spin caloritronics and magnon spintronics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.