Researchers have demonstrated for the first time that a novel class of materials, known as ferroaxials, can be rapidly and reliably switched between two stable states using light. This achievement, accomplished by a team at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) and the University of Oxford, overcomes a critical barrier to the practical use of these materials, opening a promising avenue for the development of next-generation non-volatile data storage that is both exceptionally fast and highly robust.
The new method employs single, ultrashort flashes of circularly polarized terahertz light to flip the material’s structural orientation between clockwise and counterclockwise patterns. This light-driven control provides a way to write and rewrite information without the drawbacks of current memory technologies, such as the slow speed of magnetic storage or the instability of electric-based systems. By establishing a reliable mechanism for manipulating ferroaxial states, this breakthrough paves the way for memory devices that are more durable, faster, and more energy-efficient than existing solutions, potentially transforming consumer electronics, data centers, and high-performance computing. The findings were formally published in the journal Science.
Limitations of Conventional Data Storage
Modern digital technology is built upon ferroic materials—solids that can be consistently switched between two distinct states to represent the binary code of 0s and 1s. The most common examples are ferromagnets, used in hard disk drives, and ferroelectrics, used in some types of random-access memory. Ferromagnets store data by aligning their magnetization in opposite directions, while ferroelectrics use opposite electric polarizations. These states can be readily manipulated with external magnetic or electric fields, which has made them the cornerstones of the digital age for decades.
Despite their widespread use, these conventional materials face fundamental physical limits. Ferromagnets, while reliable, suffer from relatively low switching speeds, which creates a bottleneck in accessing and writing data. Furthermore, their magnetic fields can be disturbed by external forces, posing a risk to data integrity. Ferroelectrics, on the other hand, can be switched much faster but are often unstable. Their electric polarization can be neutralized by the depolarizing response of the surrounding material, making it difficult to maintain the stored information over time without a constant power source. These inherent weaknesses have motivated a sustained scientific search for new classes of materials that could offer greater stability and performance.
A More Stable Ferroic Alternative
Ferroaxial materials represent a recently discovered addition to the ferroic family that circumvents these issues. First conceptualized in 2011 by Professor Paolo Radaelli at the University of Oxford, this class of materials does not rely on net magnetic or electric states. Instead, they are composed of microscopic vortices of electric dipoles. These dipole arrangements can be oriented in two opposite directions—either a clockwise or an anti-clockwise texture—to represent binary data. This unique structural property means they do not produce the stray magnetic or depolarizing electric fields that make other materials vulnerable.
The absence of these external fields makes ferroaxial materials exceptionally stable and resilient. Once information is set in a ferroaxial solid, it is not easily disturbed, making them ideal candidates for long-term, non-volatile data storage. However, this same stability has been their greatest challenge. The lack of a net magnetic or electric charge means they do not respond to conventional magnetic or electric fields, leaving scientists with no practical way to manipulate their state. This difficulty in controlling the clockwise and anti-clockwise orientations has, until now, limited their exploration and prevented their use in any real-world applications.
Harnessing Light to Control a New Material
The joint research team from MPSD and Oxford, following a theoretical proposal from Professor Radaelli and DPhil student Zhiyang Zeng, successfully addressed this control problem. Their experiments focused on a specific ferroaxial crystal called rubidium iron dimolybdate (RbFe(MoO4)2). They demonstrated that the ferroaxial domains within this material could be precisely and reversibly switched on demand.
A Terahertz Light-Based Method
The solution did not involve a conventional static field but rather the dynamic force of light. The researchers used single, ultrashort pulses of circularly polarized light in the terahertz frequency range. This specialized light has a twisting electric field, which can be polarized to rotate in either a right-handed or left-handed direction. The team discovered that these pulses could selectively interact with the crystal lattice of the rubidium iron dimolybdate, providing the force needed to flip its ferroaxial state from one orientation to the other.
Creating a Synthetic Control Field
According to lead author Zhiyang Zeng, the mechanism works by creating a “synthetic effective field” within the material. When the circularly polarized terahertz pulse strikes the crystal, it drives the ions in the lattice to move in circles. This ionic motion, in turn, generates a powerful internal force that couples directly to the material’s ferroaxial state. This synthetic field acts on the dipole vortices in the same way a magnetic field switches a ferromagnet or an electric field reverses a ferroelectric. By carefully tuning the properties of the light pulse, the researchers could exert precise control over a material that was previously considered inert to external manipulation.
The Mechanism of Ultrafast Switching
The direction of the switch—from clockwise to anti-clockwise or vice versa—is determined by the helicity, or twist, of the terahertz light pulse. By adjusting the polarization of the light, the researchers could selectively stabilize either a clockwise or an anti-clockwise arrangement of the electric dipoles. This binary control is the fundamental requirement for storing digital information. A pulse with one type of helicity writes a “1,” while a pulse with the opposite helicity writes a “0.”
Dr. Michael Först, a fellow author from MPSD, explained that this technique enables information storage in the two distinct ferroic states. Because the ferroaxial material is free from the depolarizing fields that plague ferroelectrics, these states are non-volatile, meaning they persist indefinitely without power. The switching process itself is also incredibly fast, occurring on the timescale of the light pulse, which is far quicker than the switching speeds achievable in magnetic hard drives.
Implications for Future Technology
This discovery is a significant step toward developing a new class of memory technology that is simultaneously fast, stable, and energy-efficient. Professor Andrea Cavalleri, who led the research team, described the work as an “exciting discovery that opens up new possibilities for the development of a robust platform for ultrafast information storage.” The ability to control these highly stable materials removes the primary obstacle that has prevented their practical application.
The research also highlights the growing potential of using tailored light fields to control exotic phases of matter. The concept of using circular phonon fields, first achieved by Cavalleri’s group in 2017, is now emerging as a powerful tool for manipulating quantum materials in ways that were not previously possible. While commercial applications are not imminent, this fundamental breakthrough provides a clear proof-of-concept. Future research will likely focus on identifying other ferroaxial materials and refining the optical techniques needed to integrate them into workable memory devices, potentially leading to a new generation of data storage technologies that can meet the growing demands of the digital world.