Regensburg 2025 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 1: Focus Session: Magnetic Phenomena from Phonon Chirality and Angular Momentum I (joint session MA/TT)

TT 1.4: Invited Talk

Monday, March 17, 2025, 11:15–11:45, H20

Phonon thermal Hall effect — •Kamran Behnia — Ecole Supérieure de Physique et de Chimie Industrielles, Paris, France

In insulating solids and liquids, heat is carried by phonons. The phonon scattering time is close to the so-called Planckian time near the melting temperature. It increases with cooling, as phonon-phonon Umklapp scattering events rarefy. A rigorous determination of thermal conductivity of insulators from first principles has been a major accomplishment of the quantum theory of solids. In contrast, our understanding of momentum and energy exchange between phonons at low temperatures is imperfect. In this context, the experimental detection of phonon thermal Hall effect in a growing number of insulators is a challenge to the condensed matter theory. The list now includes elmental insulators, such as black phosphorus, silicon and germanium, in which the spin degree of freedom is irrelevant and the atomic bonds are covalent. We will examine how magnetic field can influence anharmonicity.