Chirality-Induced Phonon Dispersion in a Noncentrosymmetric Micropolar Crystal

• Published in: Physical review letters 2020-12, Vol.125 (24), p.245302-245302, Article 245302
• Main Authors: Kishine, J, Ovchinnikov, A S, Tereshchenko, A A
• Format: Article
• Language: English
• Subjects: Chirality; Circular polarization; Crystallization; Crystals; Elastic media; Elementary excitations; Fluids; Helium; Liquid helium; Phonons; Rotons; Subsystems; Superfluidity
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.125.245302

Features of the phonon spectrum of a chiral crystal are examined within the micropolar elasticity theory. This formalism accounts for not only translational micromotions of a medium but also rotational ones. It is found that there appears the phonon band splitting depending on the left- and right-circular polarization in a purely phonon sector without invoking any outside subsystem. The phonon spectrum reveals parity breaking while preserving time-reversal symmetry, i.e., it possesses true chirality. We find that hybridization of the microrotational and translational modes gives rise to the acoustic phonon branch with a "roton" minimum reminiscent of the elementary excitations in the superfluid helium-4. We argue that a mechanism of this phenomena is in line with Nozières' reinterpretation P. Nozières, [J. Low Temp. Phys. 137, 45 (2004)JLTPAC0022-229110.1023/B:JOLT.0000044234.82957.2f] of the rotons as a manifestation of an incipient crystallization instability. We discuss a close analogy between the translational and rotational micromotions in the micropolar elastic medium and the Bogoliubov quasiparticles and gapful density fluctuations in ^{4}He.