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A laser-driven martensitic transformation in a particular Ni-Mn-Ga-based epitaxial thin film unfolded on a sub-nanosecond timescale: researchers report about 100 picoseconds for the forward change from martensite to austenite and a nearly complete forward-and-reverse cycle within 5 nanoseconds. The 100-ps figure is limited by the duration of the X-ray probe pulse, however, so it is not a precise measurement of the transformation’s intrinsic minimum time.
What changed, and how quickly?
Yuru Ge and colleagues studied a thin, epitaxial film based on nickel, manganese, and gallium (Ni-Mn-Ga), a material that can change between two crystal structures. In the low-temperature martensitic phase, the crystal structure is distorted relative to the higher-symmetry austenitic phase. The authors used a 270-femtosecond laser pulse to excite the film and followed its structural response with time-resolved synchrotron X-ray diffraction.
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They report that the forward martensite-to-austenite transformation takes about 100 picoseconds. The film then returns toward martensite, with a nearly complete martensite-to-austenite-to-martensite cycle occurring within 5 nanoseconds under the reported experimental conditions. These are results for this film and experiment, not a general speed limit for martensitic alloys or a demonstrated switching time for a practical device.
Why the 100-picosecond result is a limit, not an exact stopwatch reading
In a time-resolved diffraction experiment, the laser pulse initiates the change and short X-ray probe pulses take snapshots of the structure at selected delays. The probe pulse has a finite duration: if the structural change is as fast as, or faster than, that measurement window, the recorded response cannot resolve its true duration precisely.
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For this study, the authors identify the approximately 100-ps martensite-to-austenite timescale as limited by the synchrotron probe-pulse duration. It therefore shows that the observed transition occurs at roughly that timescale or faster within the experiment’s temporal resolution; it does not establish that the material intrinsically requires exactly 100 ps. The laser’s 270-fs duration describes the excitation pulse, not the duration of the structural transformation.
How diffraction tracks a phase transformation
Martensite and austenite have different crystal structures, and those differences change the way each phase diffracts X-rays. By measuring diffraction as the delay after laser excitation changes, researchers can track structural evolution rather than infer a phase change from temperature alone. The experiment’s time resolution depends on the X-ray probe pulse, so the duration of the pump pulse and the duration of the measured structural response are distinct quantities.
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To compare this result with another ultrafast phase-change study, useful details include the sample’s composition and thickness, its substrate and buffer layers, the laser excitation conditions, the X-ray pulse duration and time resolution, the structural signal measured, and whether the reported time covers only the forward transition or a reversible cycle. Temperature history and mechanical strain also matter for interpreting the response.
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Heating from the laser is central to the film’s evolution, and the authors measured and calculated how its temperature changed. But they also measured time-dependent strain and concluded that thermal stress in the film competes with temperature’s influence on the transformation. In the authors’ words, “in addition to temperature, thermal film stress must be considered as a competing influence on the martensitic transformation.”
This matters because a thin film is mechanically constrained by the structure beneath it. As the film heats and changes shape, the resulting stress can affect how the structural transformation proceeds. The reported response therefore cannot be understood from temperature evolution alone.
What the simulations suggest about the delay
The team also used molecular-dynamics simulations with machine-learned force fields adapted to density-functional-theory calculations. Their simulations indicate that producing the large structural distortion requires many atoms in the microstructure to move collectively, which delays completion of the transformation.
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This is the simulations’ proposed interpretation of the delay, not proof that every martensitic transformation follows the same mechanism. It helps explain why an ultrashort trigger pulse does not mean the entire crystal structure changes in the same fraction of a picosecond.
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What the result does—and does not—establish
The paper, “Sub-nanosecond structural dynamics of the martensitic transformation in Ni-Mn-Ga,” was posted by Yuru Ge and colleagues as an arXiv preprint on September 8, 2025. The authors described the nearly complete cycle within 5 ns as the fastest martensitic transformation reported at the time of that preprint. That is an author-reported comparison, not an independently replicated speed record established by the sources available here.
The clearest conclusion is narrower and more useful: in this specific laser-excited Ni-Mn-Ga-based epitaxial film, diffraction captured a very rapid forward transformation and a nearly completed return within 5 ns, while the probe pulse limited the precision of the roughly 100-ps forward-transition estimate. The measurements and simulations also show why temperature and film stress must be considered together when interpreting such dynamics.
Where to find the data and code
The associated HZDR RODARE “Data and code publication” record deposits the paper’s raw data and code. Its record DOI is 10.14278/rodare.4112; the record was published on November 13, 2025, and notes a newer version dated May 12, 2026.
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