Chiral phononics: Controlling electronic phases with phonon angular momentum

Introduction

This project aims to establish a new paradigm in the ultrafast control of solids, by using the angular momentum of chiral lattice vibrations (chiral phonons) to manipulate, induce, and switch electronic phases.

Background

The properties of solids are fundamentally determined by the crystal-lattice geometry. Developments of ultrashort terahertz and mid-IR pulses in the past decade have made it possible to dynamically modify the crystal structure by resonantly driving coherent phonons. These phonons exchange energy and momentum with the electrons, modifying interactions that are dependent on the distance between the atoms.

Chiral Phonons

Chiral phonons, in turn, have mostly been regarded as a dissipation channel for electronic angular momentum and only recently been used for ultrafast control of solids, following seminal theoretical predictions of me and my colleagues. The reason for this is rooted in two challenges:

1. The lack of feasible protocols to coherently excite chiral phonons across the Brillouin zone.
2. The complexity of angular momentum coupling processes out of equilibrium.

Project Goals

CHIRALPHONONICS will address these challenges by bridging the gap between phonon angular momentum theory and ultrafast dynamical simulations. My team and I will investigate how phonon angular momentum can be coherently generated coupled to electronic, spin, and orbital degrees of freedom that are connected to functional properties, including topological and ferroic order.

Methodology

We will combine microscopic modeling with first-principles calculations to create effective ab-initio informed models that allow us to both predict novel fundamental coupling mechanisms as well as realize quantitative materials implementations.

Expected Outcomes

This research will lead to new functionalities in solids and design principles for quantum materials out of equilibrium. Pioneering the field of ultrafast chiral phononics will open an avenue towards technologies based on phonon angular momentum switching of electronic states.