Tuning Chirality in Crystals
A chiral object has a distinct handedness, which means that it doesn’t overlap with its mirror image. If chirality could be controlled, new properties and functionalities in materials could be realized. Now Martin Gutierrez-Amigo at Aalto University in Finland and his colleagues have proposed a way to use external stimuli, such as electric fields, pressure, or temperature, to tune chirality in certain crystals [1].
Gutierrez-Amigo and his colleagues studied niobium oxide dichloride (NbOCl2), a van der Waals material with ferroelectric and nonlinear optical properties. Unusually, this material has both a chiral phase and an achiral phase. The main structural difference between the two phases is due to distortions, which could be mediated by a modulation in electron density called a charge-density wave. That possibility suggests that the material can potentially transform from one phase to the other and from one chiral form, or enantiomer, to the other.
The researchers used first-principles calculations to explore the connections between the chiral and achiral phases. They identified a third phase, an achiral intermediate phase, that functions as a bridge between the two phases and between the two enantiomers. Thanks to orientation effects, applying an electric field lowers the energy of one enantiomer relative to the other, making it more favorable. Moreover, calculations revealed that adjusting temperature or pressure can also change the energy barrier, thus potentially facilitating the transition.
Gutierrez-Amigo says that the investigation to control chirality underscored the role of structural transitions in how chirality emerges in crystals in the first place. Furthermore, the mechanism to switch between enantiomers is likely not unique in NbOCl2. Other materials in the same material family could potentially be controlled in the same way.
–Tianhan Liu
Tianhan Liu is an Associate Editor of Physical Review Letters and Physical Review Materials.
References
- M. Gutierrez-Amigo et al., “Emergent chirality and enantiomeric selectivity in layered NbOX2 crystals,” Phys. Rev. Lett. 136, 166605 (2026).