Observation of Phonon Angular Momentum

Abstract

Angular momentum (AM), a fundamental concept describing the rotation of an object about an axis, profoundly influences all branches of physics. In condensed matter, AM is intimately related to the emergence of topological quantum states, including chiral superconductivity and quantum spin liquids, and various chiral quasiparticles. Recently, it has been predicted that microscopic lattice excitations, known as phonons, can carry finite AM with remarkable macroscopic physical consequences. However, the direct observation of phonon-AM has not been achieved. In this letter, we report the experimental discovery of phonon-AM in the chiral crystal Tellurium. We show that due to AM conservation, applying a time-reversal symmetry breaking thermal gradient along the chiral axis of single crystal Te results in a macroscopic mechanical torque, $\tau$, that can be observed using a cantilever-based device. We establish that the mechanical torques change sign by flipping the thermal gradient and disappear in polycrystalline samples that lack a preferred chirality. Based on our experimental settings, we estimate $\tau \sim 10^{-11}$N$\cdot$m, in agreement with theoretical calculations. Our results uncover phonon-AM and pave the way for phonon-AM enabled quantum states for microelectronic applications.

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Cited by in corpus (10)

• Chiral Phonons in 2D Halide Perovskites
• Comprehensive Study of Phonon Chirality under Symmetry Constraints
• Magnetic Signature of Chiral Phonons Revealed by Neutron Spectroscopy in Ferrimagnetic Fe${}_{1.75}$Zn${}_{0.25}$Mo${}_3$O${}_8$
• Catalogue of chiral phonon materials
• Thermal Einstein-de Haas Effect Induced by Chiral Phonons in Carbon Nanotubes
• Observation of angular momentum transfer among crystal lattice modes
• Chiral Phonons Arising From Chirality-Selective Magnon-Phonon Coupling
• Supercurrent-induced phonon angular momentum
• D-Wave Phonon Angular Momentum Texture in Altermagnets by Magnon-Phonon Hybridization
• Symmetry-protected topological polarons