Chirality is a property of asymmetry that exists when an object or system cannot be superimposed onto its mirror image, no matter how much rotation or translation is applied. An everyday example is the asymmetry between the left and right hands: although both are similar, they are not identical, and you cannot align the two perfectly with one another. This concept is present not just in everyday objects, but also at a fundamental level in the field of physics, particularly with regard to crystals. In chiral crystals, the arrangement of atoms in a crystal structure creates a specific handedness (either left- or right-handed), which can significantly affect the material’s properties, such as its optical behavior or conductivity. The significance of chirality extends beyond the fundamental concept; it influences many technologies, including optics and electronics.
However, an interesting class of materials called non-chiral crystals can take on chiral-like properties under certain circumstances, providing valuable insight into the dynamic nature of materials. A recently published study in Science, led by Andrea Cavalleri of the Max-Planck-Institut for the Structure and Dynamics of Matter, focused on an unusual category of non-chiral crystals called antiferro-chirals. By manipulating these materials with terahertz light, the team demonstrated a new way to induce chirality in a material that would otherwise lack it, opening new possibilities for technological advancements, particularly in areas like ultrafast memory devices and optoelectronics.
Understanding Antiferro-Chirals
Antiferro-chirals, a term coined in the study, are crystals whose atomic or molecular structure might look similar to antiferromagnetic materials. In antiferromagnetic materials, magnetic moments (i.e., the spins of electrons) are arranged in a staggered, alternating pattern, causing the material’s net magnetization to cancel out. While these materials don’t display permanent magnetization as ferromagnets do, they still possess distinctive properties due to this internal structure.
An antiferro-chiral crystal is characterized by having two substructures within a unit cell—one corresponding to a left-handed configuration and the other corresponding to a right-handed configuration. These substructures are arranged in a balanced, anti-aligned manner, meaning that when combined, the overall structure is non-chiral. In other words, on a large scale, the material lacks any inherent chirality, despite the smaller units within it.
What makes these materials intriguing is their potential for induced chirality. Given the presence of left- and right-handed subcomponents within the same material, the researchers focused on how they could manipulate these materials on a ultrafast timescale to induce chiral properties. This effort marked a critical step toward understanding how matter could be dynamically controlled at the atomic level.
Inducing Chirality with Terahertz Light
The key to this breakthrough lies in the concept of nonlinear phononics, an approach that involves manipulating a material’s atomic lattice vibrations by applying specific external energy in the form of terahertz radiation. Phonons are quantum mechanical representations of vibrational energy in the lattice of a material. By exciting specific phonon modes (vibrational frequencies) within a material, researchers can cause atoms in the crystal lattice to shift, altering the arrangement and, potentially, the symmetry of the crystal.
In this study, the team at the Max-Planck-Institut for the Structure and Dynamics of Matter (MPSD), including Zhiyang Zeng as the lead author, applied a terahertz light pulse to a sample of boron phosphate (BPO4), a non-chiral material. Terahertz light, which lies between microwaves and infrared light on the electromagnetic spectrum, has been found to interact with materials in novel ways. Its application here serves as an excellent demonstration of its ability to influence and control the atomic structure of materials.
By carefully selecting a terahertz frequency that matched a specific vibrational mode of the material, the team created a shift in the crystal lattice. These vibrations were carefully coordinated to introduce a directional imbalance within the material, effectively inducing a chiral state within the crystal. This induced chirality was significant in that it was not static, but rather persisted for a very short duration—lasting on the order of several picoseconds—before the material returned to its original, non-chiral state.
The Impact of Terahertz Light Control
One of the most exciting aspects of the study is the team’s demonstration that the polarization of the terahertz light can be used to determine the direction of the chirality that is induced in the material. As Michael Först, another author of the paper, explains, by rotating the polarization of the terahertz pulse by 90 degrees, the researchers could selectively control whether the induced chirality was left-handed or right-handed. This ability to toggle between different states of chirality opens up new avenues for applications where control of material properties on very fast timescales is crucial.
For instance, this work demonstrates how external light pulses, at specific terahertz frequencies, can be used not only to trigger new states of a material, but also to enable control of those states with ultrafast precision. This new level of dynamic control could be key to creating more sophisticated optoelectronic devices, where properties like chirality directly influence the functionality of electronic or optical systems.
Potential Applications in Technology
The discovery of how to manipulate chirality in non-chiral materials could have numerous potential applications, particularly in the field of ultrafast electronics. The ability to induce chiral structures rapidly—on the order of picoseconds—could lead to next-generation memory devices. Materials with induced chirality could provide new methods for storing and transmitting information more efficiently than conventional technologies.
Moreover, dynamic control of chirality on such short time scales could enable optical switches and light-manipulating devices that function at ultra-high speeds, possibly improving devices that require manipulation of light polarization, such as in telecommunications or imaging systems. Additionally, this ability to dynamically switch the handedness of a material could lead to new developments in quantum computing, where controlling subtle material properties is essential for qubit manipulation and coherence.
Furthermore, the concept could transform the way we think about functional materials. Many materials exhibit different properties depending on their chiral configuration, and by introducing chirality dynamically, it could be possible to develop materials that can perform different functions depending on their environment or the light they are exposed to. These advances in terahertz-controlled materials may pave the way for smart materials that change properties dynamically to meet specific needs, particularly in high-tech industries.
Conclusion
The discovery of inducing chirality in non-chiral materials, like boron phosphate, through terahertz light manipulation marks a significant breakthrough in material science. By leveraging nonlinear phononics and carefully controlling the polarization of terahertz light, the researchers were able to induce left- or right-handed chirality in a non-chiral crystal, with the effect persisting for several picoseconds. This opens up new possibilities for dynamic control of material properties on ultrafast timescales, paving the way for advancements in ultrafast memory devices, optoelectronics, and quantum computing. The ability to manipulate chirality dynamically could lead to the development of highly responsive, adaptable materials with a range of applications in technology. As research in this area continues, the potential for creating smarter, faster, and more efficient devices becomes increasingly tangible, with implications for industries ranging from telecommunications to advanced computing, positioning this discovery as a significant milestone in the future of modern electronics and material innovation.
Reference: Z. Zeng et al, Photo-induced chirality in a nonchiral crystal, Science (2025). DOI: 10.1126/science.adr4713