Chiral phononics with X-ray techniques

Date

Dec 18, 2024

Time

11:00 AM - 12:00 PM

Speaker

Dr. Hiroki Ueda

Affiliation

Center for Photon Science, Paul Scherrer Inst. (PSI), Schweiz

Language

en

Main Topic

Materialien

Host

Grit Rötzer

Description

Chirality is the universal concept of defining the handedness of an object, relevant in different fields, e.g., biology, chemistry, and particle physics. In condensed matter physics, chiral (quasi-)particles are of recent central interest, e.g., chiral fermions, because of their correlation with emergent phenomena and topology. Chiral phonons, sometimes called circular phonons or phonons with angular momentum, have attracted the recent rapidly growing interest in the field. Their angular momentum naturally makes the phonon magnetic. Indeed, coherent excitation of chiral phonons was reported to create a large quasi-DC effective magnetic field [1-3]. Their magnetic character naturally links magnetism and lattice, and potentially results in emergent phenomena and non-trivial approaches to spin-lattice coupling via light-matter interaction. Despite the significant interest, their definition has been ambiguous. The definition of chirality is all the roto-inversion symmetry breaking, i.e., space-inversion symmetry and mirror symmetry. A two-dimensional rotational mode, e.g., one at the Γ point [1-3] and one propagating in the rotational plane [4], cannot be chiral because the rotational plane is a mirror plane from the symmetry point of view. Chiral phonons must be three-dimensional, which is possible when a rotational mode has a propagation perpendicular to the rotational plane. Here, we demonstrate the presence of chiral phonons in a prototypical chiral crystal, quartz, and ferroelectric crystal, LiNbO3, by means of resonant inelastic X-ray scattering (RIXS) with circularly polarized X-rays [5, 6]. Since both chiral phonons and circularly polarized X-ray photons possess angular momentum, the RIXS process needs to preserve total angular momentum, enabling us to excite chiral phonons based on the selection rule. We disclosed that circularly polarized X-rays couple to chiral phonons at general momentum points in reciprocal space, which, in principle, allows us to measure chiral phonon dispersion. I will also talk about the future perspective of chiral phononics based on X-ray techniques. [1] J. Luo et al., Science 382, 698-702 (2023). [2] M. Basini et al., Nature 628, 534-539 (2024). [3] C. S. Davies et al., Nature 628, 540-544 (2024). [4] H. Zhu et al., Science 359, 579-582 (2018). [5] H. Ueda et al., Nature 618, 946-950 (2023). [6] H. Ueda et al., in preparation.

Links

• Seminars at the IFW

Last modified: Dec 18, 2024, 7:39:52 AM