Researchers show that terahertz light can induce chirality in a non-chiral crystal

Researchers at the University of Oxford and the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) have shown that terahertz light can induce chirality in a non-chiral crystal, allowing either left- or right-handed enantiomers to emerge on demand. The finding, reported in Science, on 23 January opens up exciting possibilities for exploring novel non-equilibrium phenomena in complex materials.

Chirality is a fundamental property of matter that determines many biological, chemical and physical phenomena. It refers to objects that cannot be superimposed to their mirror images through any combination of rotations or translations, much like the distinct left and right hands of a human. In chiral crystals, the spatial arrangement of atoms confers a specific "handedness", which, for example, influences their optical and electrical properties.

Chiral solids, for example, offer exciting opportunities for catalysis, sensing and optical devices by enabling unique interactions with chiral molecules and polarized light. These properties are established when the material is grown, that is, the left- and right-handed enantiomers cannot be converted into one another without melting and recrystallization. Until now, inducing chirality using light had never been demonstrated, but it follows directly from a set of theoretical predictions made by co-author Professor Paolo G Radaelli (Department of Physics , Oxford, and Professorial Fellow in Physics, Wadham) in 2018. A collaboration between Oxford (Radaelli) and the Max Planck society (Cavalleri) led to a series of state-of-the-art experiments to test this theory.

In the new study, the Hamburg-Oxford team proved the prediction and succeeded in inducing chirality in a non-chiral material (boron phosphate, BPO4), on ultrafast timescales, using terahertz light.

Lead researcher Andrea Cavalleri (MPSD and Oxford) said: "This discovery opens up new possibilities for the dynamical control of matter at the atomic level. We are excited to see potential applications of this technology and how it can be used to create unique functionalities. The ability to induce chirality in non-chiral materials could lead to new applications in ultrafast memory devices or even more sophisticated optoelectronic platforms."

Zhiyang Zeng is a graduate student on the Oxford-Max Planck graduate training programme in quantum materials, jointly supervised by Radaelli and Cavalleri, and is the lead author on the paper: “We exploit a mechanism termed nonlinear phononics. By exciting a specific terahertz frequency vibrational mode, which displaces the crystal lattice along the coordinates of other modes in the material, we created a chiral state that survives for several picoseconds.”

Co-author Dr Michael Först (MPSD) continued: “Notably, by rotating the polarization of the terahertz light by 90 degrees, we could selectively induce either a left- or right-handed chiral structure.”

Professor Radaelli commented: “This approach has huge potential. We have already demonstrated the magnetic analogue of this effect, using light to generate magnetism in a non-magnetic material. We are currently attempting to ‘switch on’ other properties, such as ferroelectricity, on ultra-fast timescales.”

Although concerns have been raised that the ability to generate chiral molecules presents potential risks to life, in this case no permanently chiral molecule is created. Instead, crystals are induced to be right- or left-handed for an extremely short time (typically a trillionth of a second).

This work received financial support from the Deutsche Forschungsgemeinschaft via the Cluster of Excellence ‘CUI: Advanced Imaging of Matter’. The MPSD is a member of the Center for Free-Electron Laser Science (CFEL), a joint enterprise with DESY and the University of Hamburg.

For media enquiries and interview requests, contact Prof Andrea Cavalleri, .

The study ‘Photo-induced chirality in a nonchiral crystal’ will be published in Science at 19:00 GMT / 14:00 ET Thursday 23 January 2025, DOI: 10.1126/science.adr4713.