On Monday, November 25, 2024, at 12:00 c.t., the next date of our physics colloquium will take place this winter semester.
Prof. Dr. Gaël Grissonnanche, Assistant Professor at the École Polytechnique, talks about "CHIRAL PHONONS IN QUANTUM MATERIALS REVEALED BY THE THERMAL HALL EFFECT".
Phonons are quantized vibrations of atoms in a crystal, acting like tiny sound waves that propagate through solids. They are everywhere because they arise naturally from the thermal motion of atoms and govern heat, sound, and even electron behavior in materials. Understanding phonons is crucial for technologies like semiconductors, superconductors, and thermoelectrics. Surprisingly, it is becoming evident that phonons interact with magnetic fields in ways we did not expect. Indeed, we learned recently that phonons could produce a large thermal Hall effect across a wide range of quantum materials, from cuprate superconductors [1,2] to titanates [3], iridates [4], and frustrated magnets [5]. The thermal Hall effect represents the deflection of a heat current by a perpendicular magnetic field. It is usually interpreted as coming from mobile hot electrons deflected by the Lorentz force. While trivial in metals, this effect is now found in insulators. Phonons that carry no charge and, therefore, should not couple to the magnetic field are responsible for it. Phonons are the most common low-energy excitations in solids. Yet the handedness they acquire in a magnetic field - which triggers the thermal Hall effect - remains an enigma that fuels experimental and theoretical developments. In this talk, I will present the results that have led to the emergence of a new field of research aimed at discovering the origin of the thermal Hall effect of phonons and how this might relate to the question of chiral phonons measured by other probes.
[1] Grissonnanche et al. Nature 571, 376 (2019)
[2] Grissonnanche et al. Nat. Phys. 16, 1108 (2020)
[3] Li et al. Phys. Rev. Lett. 124, 105901 (2020)
[4] Ataei et al. Nat. Phys. 20, 585 (2024)
[5] Lefrançois et al. Phys. Rev. X 12, 021025 (202)
Abstract of the lecture by Prof. Gissonnanche.
The introduction will be made by Prof. Dr. Anna Böhmer.
The faculty cordially invites all interested parties. The event will take place in lecture hall HZO 20.
All dates of the Physics Colloquium can be found here.
Image: Gaël Grissonnanche