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Imagine a building that transforms from a quiet administrative office into a bustling factory within a fraction of a second, without a single brick being moved. Only what the people inside are doing changes. An international team of physicists has now achieved something remarkably similar - albeit at the level of electrons.

Using ultrashort laser pulses, researchers have altered the electronic properties of the semiconductor tin telluride (SnTe) without changing its chemical composition or atomic structure. "A semiconductor is the fundamental material behind today's computer electronics and microchips. It occupies a middle ground – on its own, it does not conduct electricity, but under the right stimulus, it begins to behave like a conductor," explained Ján Minár, Head of the Advanced and Quantum Materials Research Group and Deputy Director of the NTC Research Center. The ultrashort laser pulses temporarily drove the material into a Floquet topological state. In this state, the bulk of the material remains insulating, while its surface becomes electrically conductive, much like a metal.

The findings were published in Nature Physics, a journal that accepts only studies representing significant advances in the field. "The key finding is that a semiconductor can be transformed into a metal simply by shining light on it. The material's chemical composition and atomic structure remain completely unchanged," said Claude Monney of the University of Fribourg, Switzerland.

From a physicist's perspective, tin telluride is a particularly fascinating material because it lies very close to the boundary between two distinct electronic phases. As a result, only a small external stimulus is needed to produce a substantial change in its electronic properties. The researchers provided precisely such a stimulus using femtosecond laser pulses—bursts of light lasting only quadrillionths of a second. This approach is known as Floquet engineering. Rapid periodic driving, such as that produced by intense laser fields, creates entirely new, artificial quantum states that do not normally occur in nature. Rather than heating the material or subjecting it to high pressure, researchers use ultrafast optical control to manipulate electron behavior almost on demand.

While the experimental work was carried out primarily in Switzerland, France, and Austria, researchers from the NTC Research Center at the University of West Bohemia provided crucial theoretical support. Their calculations and computer simulations enabled them to correctly interpret the experimental data and explain the mechanism underlying the observed phenomenon. "Our task was to develop a theoretical model and calculate what happens to the electronic structure of tin telluride when it is exposed to such an intense light field," said Ján Minár. "Our young colleague, Aki Pulkkinen, made an outstanding contribution by helping to uncover the mechanism behind this light-induced phenomenon. We demonstrated that Floquet engineering can modify the behavior of electrons in the same way that would otherwise require changing the material's temperature or applying high pressure."

If similar phase transitions can eventually be induced more easily and without unwanted heating of the material, they could pave the way for a new generation of electronic devices - from ultrafast light-controlled optical switches and revolutionary quantum sensors to advanced photonic chips. For now, however, such practical applications remain a matter for future research.

A link to the full article and the complete list of authors of the Nature Physics publication.