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Chirality-Induced Phonon Dispersion in a Noncentrosymmetric Micropolar Crystal
J Kishine1,2, A S Ovchinnikov3,4, A A Tereshchenko3
1Division of Natural and Environmental Sciences, The Open University of Japan, Chiba, 261-8586, Japan.
Physical Review Letters
|January 7, 2021
Summary
Chiral crystals exhibit phonon band splitting due to rotational and translational micromotions. This chirality in the phonon spectrum resembles elementary excitations in superfluid helium-4.
Area of Science:
- Condensed Matter Physics
- Solid State Physics
- Crystal Chirality
Background:
- Micropolar elasticity theory describes materials with coupled translational and rotational degrees of freedom.
- Chiral crystals possess unique properties arising from their asymmetric structure.
- Understanding phonon behavior is crucial for characterizing material properties.
Purpose of the Study:
- To investigate the phonon spectrum of chiral crystals using micropolar elasticity theory.
- To explore the emergence of chirality in the phonon spectrum.
- To identify potential analogies with excitations in other quantum systems.
Main Methods:
- Application of micropolar elasticity theory to chiral crystals.
- Analysis of phonon band structure, considering both translational and rotational micromotions.
- Comparison of observed phonon features with theoretical models and experimental observations in other systems.
Main Results:
- Phonon band splitting observed, dependent on circular polarization, without external subsystems.
- The phonon spectrum exhibits parity breaking while maintaining time-reversal symmetry, indicating true chirality.
- Hybridization of microrotational and translational modes leads to an acoustic phonon branch with a 'roton' minimum.
Conclusions:
- Micropolar elasticity theory provides a framework for understanding chirality in phonon spectra.
- The observed 'roton'-like minimum suggests a connection to incipient crystallization instabilities.
- Analogies are drawn between micropolar elastic micromotions and quasiparticles in superfluid helium-4.
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