Chirality is a basic characteristic of matter that influences a variety of biological, chemical, and physical processes. For instance, chiral solids present compelling possibilities in areas like catalysis, sensing, and optical devices through their distinct interactions with chiral molecules and polarized light. However, these characteristics are initially established during the growth of the material; specifically, the left- and right-handed enantiomers cannot be interchanged without undergoing melting and recrystallization.
Chirality is a basic characteristic of matter that influences a variety of biological, chemical, and physical processes. For instance, chiral solids present compelling possibilities in areas like catalysis, sensing, and optical devices through their distinct interactions with chiral molecules and polarized light. However, these characteristics are initially set during the material’s growth; specifically, left- and right-handed enantiomers cannot be interchanged without melting and recrystallization.
Researchers from the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) and the University of Oxford have discovered that terahertz light can create chirality in a non-chiral crystal, enabling either left- or right-handed enantiomers to form on command. This revelation, published in Science, presents exciting opportunities for studying new non-equilibrium behaviors in complex materials.
Chirality refers to objects that cannot be matched with their mirror images through any combination of rotation or movement, similar to how the left and right hands are different. In chiral crystals, the arrangement of atoms gives rise to a specific “handedness,” significantly affecting their optical and electrical characteristics.
The team from Hamburg and Oxford concentrated on a class of non-chiral crystals known as antiferro-chirals, which resemble antiferromagnetic materials where magnetic moments are arranged in opposite directions in a staggered manner, resulting in no net magnetization. An antiferro-chiral crystal contains equal parts of left- and right-handed substructures within a unit cell, making it overall non-chiral.
The research team, guided by Andrea Cavalleri, utilized terahertz light to disrupt this balance in the non-chiral material boron phosphate (BPO4), thereby creating tangible chirality on an ultrafast time scale. “We use a process called nonlinear phononics,” explains Zhiyang Zeng, the main author of this study. “By activating a specific vibrational mode at terahertz frequency, which shifts the crystal lattice along the pathways of other modes in the material, we established a chiral state that lasts for several picoseconds,” he continued. “Notably, by altering the polarization of the terahertz light by 90 degrees, we were able to selectively induce either a left- or right-handed chiral structure,” adds co-author Michael Först.
“This breakthrough opens new avenues for dynamically controlling matter at the atomic level,” remarks Andrea Cavalleri, the research group leader at MPSD. “We are eager to explore potential applications of this technology and how it might facilitate the creation of distinctive functionalities. The capability to create chirality in non-chiral materials could pave the way for advancements in ultrafast memory devices and advanced optoelectronic systems.”
This research was funded by the Deutsche Forschungsgemeinschaft through the Cluster of Excellence ‘CUI: Advanced Imaging of Matter’. The MPSD is also part of the Center for Free-Electron Laser Science (CFEL), a collaborative venture with DESY and the University of Hamburg.
