Universal features of canonical phonon angular momentum without time-reversal symmetry

Abstract

It is known that phonons have angular momentum, and when the time-reversal symmetry (TRS) is broken, the total phonon angular momentum in the whole system becomes nonzero. In this paper, we propose that as an angular momentum of phonons for a crystal without TRS, we need to consider the canonical angular momentum, as opposed to the kinetic angular momentum in previous works. Next, we show that the angular momentum of phonons without TRS exhibits universal behaviors near the $\Gamma$ point. We focus on in-plane oscillations in two-dimensional crystals as an example. By breaking the TRS, one of the acoustic phonon branches at the $\Gamma$ point acquires a gap. We show that the angular momentum of its acoustic phonon with a gap has a peak with the height $\pm \hslash$ regardless of the details of the system. From this, we find that this peak height changes discontinuously by changing the sign of the TRS-breaking parameter.

arXiv comment11pages, 3figures

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Cited by in corpus (8)

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• Strain-driven chiral phonons in two-dimensional hexagonal materials
• Conversion of chiral phonons into magnons in ferromagnets and antiferromagnets
• Light Driven Spontaneous Phonon Chirality and Magnetization in Paramagnets
• Anomalous circular phonon dichroism in transition metal dichalcogenides
• Spin-spin interaction mediated by chiral phonons
• Properties and challenges of hot-phonon physics in metals: MgB${}_2$ and other compounds