Strain turns non-chiral crystals left- or right-handed on demand

Researchers have uncovered a groundbreaking method to manipulate chirality in non-chiral crystals using mechanical strain, offering a novel approach to engineer materials with desired handedness on demand. According to findings published in Nature, scientists at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) and the University of Oxford demonstrated that applying controlled mechanical stress can transform otherwise symmetric crystals into structures exhibiting either left- or right-handed chirality. This discovery introduces a new class of materials known as piezochiral substances, where chirality is not inherently fixed but can be toggled through external forces. The concept of chirality refers to the inability of an object to be superimposed onto its mirror image, akin to how a left hand cannot perfectly align with a right hand. Chirality plays a crucial role in determining the behavior of light, electrons, and even biochemical interactions within crystalline structures. Traditionally, achieving chirality required complex chemical synthesis or specific growth conditions. However, this recent study shows that mechanical deformation alone can induce such properties in materials that were previously considered achiral. Zhiyang Zeng, lead author of the study, explained that unlike other material properties such as polarization or magnetization, which have well-established methods for manipulation, chirality had remained elusive in terms of direct external control. By subjecting non-chiral crystals to tensile or compressive strain, the researchers observed the emergence of optical activity, an unmistakable indicator of chirality. The direction of the applied force dictated whether the resulting structure was left- or right-handed, providing a reversible mechanism to switch between these states. Michael Först, a co-author of the paper, emphasized that the reversibility of the process allows for repeated generation, removal, and selection of chiral configurations. This capability could lead to dynamic materials whose properties change in response to mechanical inputs, opening up possibilities for adaptive technologies and responsive devices. The research team developed a comprehensive theoretical model to identify under what conditions the piezochiral effect would manifest in various crystal systems. Based on this model, they compiled an open-access database listing potential candidates for further exploration. This resource enables global researchers to investigate and develop piezochiral materials tailored for specific applications. Andrea Cavalleri, who led the research in Hamburg alongside Paolo Radaelli from the University of Oxford, described the phenomenon as the "piezochiral effect." He highlighted its potential to influence a wide range of materials, including thin films and bulk solids, enabling the creation of new chiral properties such as superconductivity. This advancement could revolutionize fields ranging from electronics to pharmaceuticals, where controlling molecular handedness is critical. The implications of this discovery extend beyond fundamental science. With the ability to dynamically alter chirality, engineers might design materials that adapt to environmental changes or perform specialized functions based on mechanical stimuli. For instance, piezochiral materials could be integrated into sensors, actuators, or energy-harvesting devices that respond to physical stresses in real time. The study underscores the importance of mechanical deformation as a tool for manipulating material properties at the atomic scale. While previous efforts focused on altering electrical or magnetic characteristics through strain, this work expands the scope to include structural asymmetry. As researchers continue exploring the piezochiral effect, they may uncover additional ways to harness mechanical forces for advanced technological applications. The publication of this research marks a significant step forward in understanding and utilizing chirality in materials science. Scientists around the world will likely build upon this foundation to develop innovative solutions leveraging the newfound ability to control handedness through mechanical means.