Abstract:
While chirality is well-established in biology, chemistry, and pharmacology, its exploration in inorganic periodic crystals is relatively recent. One of the emerging areas of focus is chiral phonons and their unique properties where the ability to tune and flip chirality remains a highly sought-after property to control [1]. While the possibility of flipping chirality by reversing polarization is known in ferroelectric-gyroelectric crystals like Pb₅Ge₃O₁₁ [2], the question remains of whether chirality can be an independent order parameter and possibly a new ferroic order.
Based on density functional theory calculations and symmetry analysis, I will show that displacive chiral phase transitions can occur and be described by the so-called soft phonon mode theory. I will illustrate this mechanism through K₃NiO₂ crystal by proving that a single unstable zone boundary phonon of the high temperature phase can drive the system into the two distinct low symmetry enantiomorphic space groups with equal energy, thereby forming a double-well energy landscape between left- and right-handed structures. I will show that this analysis can be generalized to build a systematic and high throughput search for new displacive chiral phase transitions, similarly to what was done for ferroelectric materials [4]. Furthermore, I will present potential mechanisms for flipping between these enantiomorphic phases such as strain or external fields [5]. These findings give insight onto fundamental discussions like whether chirality can be considered a new ferroic order parameter in crystals, what could be its conjugate field, etc.
[1] E. Bousquet, et al., J. Phys.: Condens. Matter 37, 163004 (2025).
[2] M. Fava, et al., Phys. Rev. B 109, 024113 (2024).
[3] M. Fava, E. McCabe, A. Romero and E. Bousquet, Phys. Rev. B 111 174102 (2025).
[4] F. Gómez-Ortiz, A. Romero and E. Bousquet, Phys. Rev. B 112, 014107 (2025).
[5] M. Fava, E. McCabe, A. Romero and E. Bousquet, arXiv:2405.12696v2 (2025).
