The study, published in the Journal of Materials Science: Metallurgy, was led by Serkan Öğüt of Marmara University together with colleagues including Tayebeh Mousavi and Tahereh Zargar of King’s College London, Yi Huang of Bournemouth University, and Terence G. Langdon of the University of Southern California. Their work is the first to demonstrate complete solid-state mixing of copper and vanadium into a bulk nanostructured composite using this method, extending a line of research that previously succeeded with other immiscible pairs such as copper-tantalum and copper-molybdenum.

The experimental approach was deceptively simple in concept. The researchers took thin disks of oxygen-free copper and pure vanadium, each ground to a thickness of 0.8 millimeters, and stacked them in a sandwich configuration with vanadium between two copper layers. These stacks were then placed between massive anvils and processed under a pressure of 6.0 gigapascals at room temperature. As the anvil rotated, the disks were twisted through numbers of turns ranging from just half a rotation all the way up to 250 full turns, generating equivalent strains so extreme that they cannot be practically achieved by any conventional deformation process.

Optical microscopy of the processed disks revealed a clear progression of mixing with increasing turns. After 10 turns the copper and vanadium layers remained sharply defined with no fragmentation. By 20 turns, the vanadium layer had begun to break apart in the outer regions of the disk, and by 50 turns substantial mixing was visible from the half-radius to the edge. Complete mixing required patience and mechanical extremity: only after 200 to 250 turns did the cross-sections take on the uniform grey appearance of a fully blended alloy, with homogenization spreading inward from the disk edges toward the center as strain accumulated.

Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed the microscopic reality behind the visible transformation. In the 200-turn sample, the copper layers contained between roughly 15 and 35 percent vanadium, evidence of mutual dissolution far beyond the equilibrium solubility, which is a mere 0.08 weight percent for vanadium in copper at room temperature. In the 250-turn sample, the edge regions showed no trace of pure copper or vanadium at all, instead forming a uniform copper-20 atomic percent vanadium solid solution, while the disk center displayed a matrix of similar composition with thin vanadium-rich layers of roughly copper-70 vanadium-30.

X-ray diffraction provided independent confirmation of the alloying. As the number of turns increased, the diffraction peaks of vanadium gradually vanished while the copper peaks shifted toward lower angles, a signature of the copper lattice expanding as larger vanadium atoms, with an atomic radius of 134 picometers versus 128 picometers for copper, substituted into the crystal structure. Quantitative analysis using Vegard’s law yielded an average vanadium concentration of approximately 19 percent across the entire disk. The copper crystallite size simultaneously collapsed to roughly 12 nanometers after 250 turns, accompanied by a lattice microstrain of about 1.7 percent, numbers that reflect the extraordinary defect density generated during processing.

Transmission electron microscopy of the 200-turn sample revealed a striking bimodal heterostructure. Coarser regions of approximately 100 nanometer grains, rich in copper with only trace vanadium, coexisted with much finer regions of 20 to 30 nanometer grains in which copper and vanadium were thoroughly mixed. The presence of straight twins and relatively few dislocations in the coarser grains indicates that dynamic recrystallization occurred during processing, continuously renewing the microstructure even as deformation ground it finer.

The mechanical consequences were dramatic. Hardness mapping showed values climbing from about 100 to 200 Hv in the barely deformed samples to a range of 350 to 400 Hv after 200 and 250 turns, substantially higher than either HPT-processed pure copper or pure vanadium. Tensile testing of the 200-turn sample after a gentle post-processing anneal at 773 Kelvin for one hour produced the headline result: an ultimate tensile strength near 1300 megapascals with 3.5 percent elongation, compared with roughly 1200 megapascals for HPT-processed pure vanadium and only about 400 megapascals for HPT-processed pure copper. The team attributes this strength to a combination of solid solution strengthening from dissolved vanadium, interface barriers to dislocation motion, Hall-Petch strengthening from nanoscale grains, and a dispersion of fine vanadium-rich grains acting somewhat like precipitate hardening.

The annealing experiments also revealed a fascinating thermal trade-off. At 773 Kelvin, hardness dropped only in the disk center, where copper-rich regions recovered preferentially while the vanadium-rich nanocrystalline zones resisted growth. At 973 and 1173 Kelvin, recrystallization swept the entire cross-section, dropping strength to about 800 and 500 megapascals respectively while boosting elongation to roughly 30 and 50 percent. This tunable strength-ductility balance, with coarse copper-rich grains contributing ductility and fine mixed grains contributing strength, mirrors the heterostructure design principles currently exciting the structural materials community.

The motivation runs deeper than record strength alone. Vanadium offers low density of 6.1 grams per cubic centimeter against 10.2 for molybdenum and 16.4 for tantalum, along with a low neutron activation cross-section, making copper-vanadium alloys attractive for high-strength electrical conductors in high-field magnets, demanding electrical contacts, and particle accelerator components. Because vanadium barely dissolves in copper under equilibrium, it can in principle strengthen the matrix without degrading electrical conductivity, though the researchers note that direct resistivity measurements on their HPT-processed alloy remain a task for future work, since severe deformation can create non-equilibrium solid solutions with different transport behavior. Whether spinning metals under gigapascals of pressure becomes an industrial route or remains a laboratory marvel, the demonstration that room-temperature torsion can rewrite the rules of alloying opens a genuinely new page in materials design.

Subject of Research: Room-temperature solid-state alloying of immiscible copper and vanadium by high-pressure torsion

Article Title: Fabrication of immiscible Cu-V alloy by high-pressure torsion

Article References: Öğüt, S., Zargar, T., Mousavi, T., Georges, L., Ghosh, S., Hamada, A., Abd-Elaziem, W., Huang, Y., & Langdon, T. G. (2025). Fabrication of immiscible Cu-V alloy by high-pressure torsion. Journal of Materials Science: Metallurgy, 1(1), Article 2. https://doi.org/10.1007/s44492-025-00002-w

Image Credits: AI Generated

DOI: 10.1007/s44492-025-00002-w

Keywords: copper-vanadium alloy, high-pressure torsion, severe plastic deformation, immiscible metals, nanostructured materials, solid solution strengthening, ultrafine grains, mechanical alloying, tensile strength, electrical conductors, vanadium, copper

Recently, a team spearheaded by Professor Andreas Tittl from Ludwig-Maximilians-Universität München (LMU) in collaboration with Monash University in Australia has broken new ground, presenting a paradigm-shifting technique that allows for the genuine on-and-off switching of optical resonances on ultrafast timescales. Their pioneering work, published in the journal Nature on August 6, 2025, showcases how precise temporal control of light-matter interaction can be achieved by engineering a novel class of metasurfaces—ultrathin layers embedded with specially designed nanostructures. This breakthrough moves far beyond the conventional, delivering a level of control and speed previously unimaginable in the field.

At the heart of this technological leap is an ingenious design strategy involving pairs of silicon nanorods, each with deliberately distinct geometrical shapes—an intentional asymmetry. While the rods differ physically, their optical responses at certain wavelengths perfectly counterbalance each other, resulting in a structure that is, paradoxically, “invisible” to the probing light. In essence, despite the physical presence of the nanoresonators, their optical resonance is effectively canceled out, putting the system into a so-called ‘dark’ state where resonance is completely switched off.

The power of this approach lies in the temporal breaking of symmetry: by using an ultrafast laser pulse lasting a mere 200 femtoseconds, researchers can selectively excite one of the dissimilar nanorods, rapidly altering its refractive or absorptive properties on a picosecond timescale. This targeted excitation disrupts the delicate optical equilibrium, instantly coupling the resonance with incoming light and effectively switching the resonance ‘on.’ This ultrafast and reversible toggling of the resonance opens tantalizing possibilities for applications demanding rapid optical modulation with minimal energy loss.

Professor Tittl emphasizes that the subtle interplay between structural asymmetry and induced optical symmetry is the centerpiece of this method. “We create a perfect optical balance within an inherently asymmetric system. By deliberately breaking this equilibrium with an ultrafast laser, we unlock an unprecedented degree of control over light-matter interactions,” he explains. This control extends not only to the presence or absence of resonance but also to fine-tuning the resonance’s bandwidth, acting as a highly responsive optical control knob.

The experimental challenges faced by the researchers were substantial. Crafting such bespoke metasurfaces required advanced nanoscale fabrication techniques carried out within class 100 cleanroom environments, utilizing top-tier lithography and etching processes to shape the silicon nanorods with nanometer precision. Equally demanding was the need to observe and measure these ultrafast dynamics experimentally. The team employed state-of-the-art time-resolved spectroscopy to track how resonances emerged and dissolved within mere picoseconds, achieving a real-time window into processes previously accessible only through simulation.

According to Leonardo de S. Menezes, who led the spectroscopic measurements, their observations delivered unequivocal evidence of the concept’s efficacy. The experiments revealed a dramatic surge in light coupling when symmetry was broken temporarily, all without introducing significant dissipative losses. This characteristic is critically important, distinguishing their technique from competing methods where switching often incurs unwanted energy dissipation, thereby limiting device performance and scalability.

The versatility of this newly demonstrated control was further highlighted by the team’s ability to perform four distinct switching operations: generating a resonance from a dark baseline state, fully quenching an established resonance, and finely adjusting the resonance profile by either broadening or sharpening it. Notably, sharpening the resonance led to an increase in its quality factor—or Q-factor—by over 150%, underscoring the precision of optical engineering achieved. The Q-factor reflects how well a resonator stores energy; higher values imply stronger confinement and less loss, essential for sensing, filtering, and quantum optics applications.

What’s particularly exciting is the generality of the principle underlying this temporal symmetry breaking. While silicon was selected for this study due to its favorable optical properties and well-established nanofabrication processes, the approach is intrinsically material-agnostic and could readily be adapted to other semiconductors, dielectrics, or even plasmonic materials. This flexibility hints at future platforms where switching speeds could be pushed even further, utilizing materials with faster carrier dynamics or nonlinear responses.

This breakthrough heralds a new frontier in active nanophotonics. Until now, on-off switching of optical resonances at ultrafast speeds was a fundamental bottleneck, curtailing the development of compact, low-loss optical switches integral to next-generation telecommunications and all-optical computing systems. Beyond these practical applications, the ability to toggle resonances cleanly and rapidly opens unexplored avenues in fundamental physics. For instance, researchers studying emergent quantum phenomena—such as time crystals, which manifest as temporally ordered states of matter—may find in these metasurfaces an ideal platform for experimental exploration.

Crucially, the demonstration of ultrafast “temporal symmetry breaking” not only enriches our understanding of light-matter interaction but also offers a powerful tool for engineering the flow of photons in nanoscale devices with unprecedented agility and minimal energy penalty. This capability aligns perfectly with the growing global demand for faster, more energy-efficient photonic components capable of integrating seamlessly into future information technologies.

As optical technologies continue to push the boundaries of speed, size, and complexity, innovations like this resonate loudly. The union of clever structural asymmetry with precise temporal control marks a transformational step towards dynamic photonic systems that can be tailored at the femtosecond level. This marriage of design and ultrafast physics promises to invigorate fields spanning from high-speed optical modulators and sensors to quantum communication and beyond.

Looking ahead, the implications of this discovery are profound. By expanding this methodology to varied materials and integrating it into complex photonic circuits, we may soon witness the rise of wholly new classes of devices that manipulate light with a finesse and speed previously confined to theoretical imagination. The genesis of resonances from silence and their annihilation on demand portend an exciting era where’s control over the photon’s dance becomes absolute—a revolution light-years ahead.

Subject of Research: Not applicable

Article Title: Optical control of resonances in temporally symmetry-broken metasurfaces.

News Publication Date: 6-Aug-2025

Web References: 10.1038/s41586-025-09363-7

Keywords

Nanophotonics, optical resonators, metasurfaces, temporal symmetry breaking, ultrafast laser pulse, silicon nanorods, optical switching, Q-factor, time-resolved spectroscopy, light-matter interaction, ultrafast modulation, photonic devices