QuIC Talk by Swati Chaudhary: Phonons with angular momentum: Magnetic properties and applications

Quantum Information and Coherence (QuIC) Talks, IIT Kanpur

Title: Phonons with angular momentum: Magnetic properties and applications
Speaker: Dr. Swati Chaudhary, University of Texas at Austin & Northeastern University, Boston, USA
Time: 4:30 - 5:30 pm; Wed, April 12th, 2023
Venue: FB-382

Abstract: The idea that photons can carry both spin and orbital angular momentum is known for more than thirty years now and has been applied in diverse fields ranging from astronomy and optical trapping to quantum information processing and data storage. Recently, the angular momentum of phonons has also attracted a lot of attention. The angular momentum of phonons can arise either from circular lattice vibrations of ions or from the relative phase difference between lattice displacements on neighboring ions. These phonons which carry angular momentum are known as chiral phonons and can respond very strongly to the magnetic field. On the basis of purely circular ionic motion, these phonons are expected to carry a magnetic moment of the order of a few nuclear magnetons. However, some recent experiments have demonstrated a phonon magnetic moment of the order of a few Bohr magnetons. This kind of giant magnetic response points towards the electronic contribution to the magnetic moment of phonons. Many diverse mechanisms have been discovered for this enhanced magnetic response of chiral phonons. The orbital-lattice coupling is one such mechanism where low-energy electronic excitations on a magnetic ion hybridize with phonons and endows a large magnetic moment to phonons. In this talk, I’ll present a microscopic model for the effective magnetic moments of chiral phonons based on this mechanism. Our model is able to reproduce the experimentally measured magnitudes in some rare-earth paramagnets and our detailed analysis also predicts that similar effects also occur in other magnetic materials. Interestingly, this intricate mechanism arising from the coupling of lattice and orbital degrees of freedom not only leads to a large magnetic response of such phonons but can also be utilized for phononic control of electronic angular momentum in magnetic materials. Such phonons with giant magneto-phononic and phono-magnetic responses can possibly be used for dissipationless thermal Hall transport, ultrafast control of quantum matter, and quantum information processing.