Physicists at the University of Konstanz have reported a method that can allow objects to "magically turn into a different material" by altering the magnetic properties of that material using light. The process, described in the journal Science Advances, could open new possibilities for data storage, high-speed information transfer, and quantum research at plain room temperature. The research team, led by Davide Bossini, demonstrated that laser pulses can coherently excite pairs of magnons - collective magnetic vibrations - in naturally occurring crystals.
A magnon is a quantum particle that represents a collective disturbance in the alignment of electron spins within a magnetic material. When one electron's spin flips, it triggers a ripple of spin changes that travels through the lattice like a wave. This wave-like excitation carries both energy and angular momentum, making magnons crucial for understanding magnetism and for potential applications in spintronics, where information is transmitted using spin rather than charge.
This excitation enables the control of magnetic frequencies and amplitudes in a way that does not rely on heat. "The result was a huge surprise for us. No theory has ever predicted it," said Bossini. By driving high-frequency magnon pairs, the team was able to influence other magnons in the material, effectively changing their magnetic properties.
The study addresses a growing challenge in information technology (IT). Sustaining the growth of the data volume generated by artificial intelligence and the Internet of Things requires new schemes for data storage and processing that operate at terahertz frequencies without being limited by thermal throttling. The optical drive of coherent magnetic collective excitations, namely magnons, represents one promising route. The ability to arbitrarily and nonthermally increase magnon frequencies with laser pulses could enable this progress, yet such an effect had not been reported until now.
To achieve it, the Konstanz team explored the optical resonant excitation of high-momentum magnons. These were experimentally observed to couple to low-momentum magnons, modifying their frequencies and amplitudes. The evidence, not caused by laser heating, is explained with a resonant light-scattering mechanism that couples high- and low-momentum eigenmodes (certain distinct periodic vibration patterns) across momentum space. According to the researchers, this mechanism discloses routes to inducing instabilities and phase transitions via mode softening, and potentially even light-driven Bose-Einstein condensation of magnons and superconductivity mediated by high-momentum spin fluctuations.
Bossini emphasized that the observed effects are not caused by heating. "The effects are not caused by laser excitation. The cause is light, not temperature," he explained. This non-thermal mechanism avoids the buildup of heat, a common obstacle in high-speed data processing. The process also alters the fundamental characteristics of the material. "Every solid has its own set of frequencies: electronic transitions, lattice vibrations, magnetic excitations. Every material resonates in its own way," said Bossini. "It changes the nature of the material, the 'magnetic DNA of the material,' so to speak, its 'fingerprint'. It has practically become a different material with new properties for the time being."
The experiments were conducted using haematite, a naturally abundant iron ore historically used in compasses. "Haematite is widespread. Centuries ago, it was already used for compasses in seafaring," Bossini noted. Unlike many advanced technologies, the method does not require rare earth elements or exotic materials.
The findings also suggest potential applications in quantum research. The method could enable the creation of light-induced Bose-Einstein condensates of high-energy magnons at room temperature. Such a development would allow the study of quantum effects without the need for extreme cooling, which is typically required at temperatures near -270 degrees Celsius. While further research is needed, the work from Konstanz demonstrates a new way to manipulate materials with light, offering a possible path toward faster, more efficient information technologies and accessible quantum experiments.
Source: University of Konstanz, AAAS
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