A team of researchers has demonstrated a novel method for controlling a unique class of materials, opening a new avenue for the development of ultra-fast, highly stable, non-volatile memory. By using focused pulses of terahertz light, scientists at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) and the University of Oxford successfully switched the orientation of microscopic structures within a crystal, a breakthrough that could fundamentally change how electronic devices store information. This achievement overcomes a major hurdle that has prevented the practical application of these otherwise promising materials.
The discovery centers on a class of solids known as ferroaxial materials, whose unique properties make them exceptionally stable and resistant to the external fields that can corrupt data in current storage technologies. Until now, this same stability made them incredibly difficult to manipulate. The new light-based control mechanism, published in the journal Science, establishes a reliable way to write and rewrite information in these materials, paving the way for memory technologies that consume less energy, operate at higher speeds, and retain data far more robustly than today’s magnetic hard drives or solid-state flash memory.
Limitations of Current Data Storage
Modern digital technology is built upon ferroic materials, which are substances that can be switched between two or more stable states to represent the binary 0s and 1s of digital information. The most common examples are ferromagnets, used in hard disk drives, and ferroelectrics, used in certain types of electronic memory. Ferromagnets store data by aligning their magnetization in opposite directions, while ferroelectrics use opposite electric polarizations to achieve the same goal. These materials have enabled the digital revolution, but they face fundamental physical limits.
Ferromagnetic memory, while reliable for long-term storage, suffers from relatively slow switching speeds, which bottlenecks performance in high-speed computing. Furthermore, the magnetic fields they generate can interfere with neighboring bits if they are packed too densely, limiting storage capacity. Ferroelectric materials offer faster switching speeds but are often plagued by instability. Their electric polarization creates depolarizing fields in the surrounding material, which can cause the stored information to degrade over time, making them unsuitable for archival or long-term, power-off storage. These weaknesses have driven a search for alternative materials that can provide both speed and stability.
A More Stable Ferroic Alternative
Ferroaxial materials represent a distinct and promising solution to these challenges. First described in 2011 by Professor Paolo Radaelli at the University of Oxford, these materials do not rely on net magnetic or electric polarization. Instead, their unique property comes from microscopic vortices of electric dipoles within the crystal structure. These vortices can be arranged in either a clockwise or a counter-clockwise pattern, providing the two stable states needed for binary data storage. A key advantage of this arrangement is that it produces no stray magnetic or depolarizing electric fields.
This internal structure makes ferroaxial materials exceptionally robust. They are inherently stable and immune to the external disturbances that can affect conventional memory. However, this same resilience has been their biggest drawback. Without a net magnetic or electric handle, controlling these clockwise and counter-clockwise states with conventional fields was deemed nearly impossible, which has limited their practical exploration until this recent breakthrough. The challenge for scientists was to find an external force precise and strong enough to toggle the rotational state without disrupting the crystal itself.
Manipulating States with Light
The research team, led by Professor Andrea Cavalleri of MPSD and Oxford, successfully addressed this control problem by using light. Their experiment focused on a specific ferroaxial crystal, rubidium iron dimolybdate (RbFe(MoO4)2). They demonstrated that single, ultrashort flashes of circularly polarized terahertz light could reliably switch the material’s ferroaxial domains between the clockwise and anti-clockwise states.
A Synthetic Crystalline Field
The mechanism behind this optical control is both elegant and powerful. The circularly polarized light pulses interact with the ions in the crystal lattice, driving them in tiny circles. According to lead author Zhiyang Zeng, this motion creates a “synthetic effective field” within the material. This transient, light-induced field is strong enough to couple directly to the rotational ferroaxial state, acting much like a magnetic field does on a ferromagnet or an electric field on a ferroelectric. It provides the necessary torque to flip the orientation of the dipole vortices from one stable configuration to the other.
Precision Through Polarization
Crucially, the direction of the switch is deterministic. By controlling the helicity, or twist, of the terahertz light, the researchers could select which state to stabilize. For instance, a right-handed circularly polarized pulse might set the ferroaxial state to clockwise, while a left-handed pulse would flip it to counter-clockwise. Dr. Michael Först, a fellow author from MPSD, explained that this technique enables the selective writing of information into the two distinct ferroic states. This level of precision is essential for creating a reliable memory device where data can be written and rewritten on demand.
New Possibilities for Information Technology
This discovery transforms ferroaxial materials from a scientific curiosity into a viable platform for next-generation non-volatile memory. Because the information is stored in the structural arrangement of the crystal and is written with light, such a device would not require any power to retain data, making it truly non-volatile and highly energy-efficient. The use of optical pulses for writing also promises switching speeds that are orders of magnitude faster than current magnetic storage technologies, operating on the picosecond timescale.
Professor Cavalleri noted that the findings open up exciting possibilities for developing a robust platform for ultrafast information storage. The stability of ferroaxial states suggests that data could be archived for extremely long periods without degradation. This could lead to archival drives that last for centuries and consumer devices with instant-on capabilities and significantly lower standby power consumption. The work also advances the broader field of materials science, demonstrating how specially tailored light fields can be used to control exotic phases of matter in ways not possible with conventional methods.