Twisting Crystals With Light: Unlocking Chirality in a Flash

By Max Planck Institute for the Structure and Dynamics of Matter January 24, 2025

Collected at: https://scitechdaily.com/twisting-crystals-with-light-unlocking-chirality-in-a-flash/

A new technique involving terahertz light has enabled the creation of chiral states in non-chiral materials, offering exciting possibilities for future technological applications.

Chirality is a key property of matter that plays a crucial role in many biological, chemical, and physical processes. In chiral solids, this property enables unique interactions with chiral molecules and polarized light, making them valuable for applications in catalysis, sensing, and optical devices. However, chirality in these materials is typically fixed during their formation—once a crystal is grown, its left- and right-handed forms, or enantiomers, cannot be switched without melting and recrystallizing it.

Now, researchers from the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) and the University of Oxford have discovered a way to induce chirality in a non-chiral crystal using terahertz light. This breakthrough allows them to create either left- or right-handed enantiomers on demand. Published in Science, this finding opens exciting new possibilities for studying and controlling complex materials in non-equilibrium conditions.

Chirality and Crystal Structure

Chirality describes objects that cannot be perfectly aligned with their mirror images, no matter how they are rotated or moved. A common example is the difference between our left and right hands. In chiral crystals, the way atoms are arranged gives the material a specific “handedness,” which can affect properties such as how it interacts with light and electricity.

Researchers from the Hamburg-Oxford collaboration studied a special class of non-chiral crystals known as antiferro-chirals. These crystals are similar to antiferromagnetic materials, where magnetic moments align in opposite directions in a staggered pattern, canceling out the overall magnetization. In an antiferro-chiral crystal, equal amounts of left- and right-handed substructures exist within each unit cell, making the overall structure non-chiral.

Breakthrough in Chirality Induction

The research team, led by Andrea Cavalleri, used terahertz light to lift this balance in the non-chiral material boron phosphate (BPO₄), in this way inducing finite chirality on an ultrafast time scale.

“We exploit a mechanism termed nonlinear phononics,” says Zhiyang Zeng, lead author of this work. “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,” he added.

“Notably, by rotating the polarization of the terahertz light by 90 degrees, we could selectively induce either a left- or right-handed chiral structure,” continues fellow author Michael Först.

Potential Applications and Future Outlook

“This discovery opens up new possibilities for the dynamical control of matter at the atomic level,” says Andrea Cavalleri, group leader at the MPSD. “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.”

Reference: “Photo-induced chirality in a nonchiral crystal” by Z. Zeng, M. Först, M. Fechner, M. Buzzi, E. B. Amuah, C. Putzke, P. J. W. Moll, D. Prabhakaran, P. G. Radaelli and A. Cavalleri, 23 January 2025, Science.
DOI: 10.1126/science.adr4713

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.