Scientists discover way to pause ultrafast melting in silicon using precisely timed laser pulses

A team of physicists has discovered a method to temporarily halt the ultrafast melting of silicon using a carefully timed sequence of laser pulses. This finding opens new possibilities for controlling material behavior under extreme conditions and could improve the accuracy of experiments that study how energy moves through solids.

The research, published in the journal Communications Physics, was led by Tobias Zier and David A. Strubbe of the University of California, Merced, in collaboration with Eeuwe S. Zijlstra and Martin E. Garcia from the University of Kassel in Germany. Their work focuses on how intense, ultrashort laser pulses affect the atomic structure of silicon — a material widely used in electronics and solar cells.

Using advanced computer simulations, the researchers showed that a single, high-energy laser pulse typically causes silicon to melt in a fraction of a trillionth of a second. This process, known as nonthermal melting, happens so quickly that atoms lose their orderly structure before they even have time to heat up. However, by splitting the laser energy into two pulses and timing them precisely, the team was able to “pause” this melting process and stabilize the material in a new, metastable state.

The simulations were performed using a technique called ab initio molecular dynamics, which models the behavior of atoms and electrons from first principles. The researchers found that the first laser pulse sets the atoms in motion, while the second pulse — delayed by just 126 femtoseconds — interferes with that motion in a way that prevents the atoms from becoming disordered. This creates a temporary state where the material remains solid, even though it has absorbed enough energy to melt.

Interestingly, this metastable state retains many of the electronic properties of the original crystal, including a slightly reduced band gap, which is important for how the material conducts electricity. The researchers also observed that the atomic vibrations, or phonons, in this state were cooler and more stable than expected, suggesting that the second pulse effectively “freezes” the atomic motion.

The study concludes that this method of using timed laser pulses could be applied to other materials that exhibit similar behavior, potentially enabling the creation of new phases of matter or improving the precision of experiments that measure how energy is transferred between electrons and atoms. The authors suggest that future research could explore how to fine-tune this technique for different materials and use it to better understand the fundamental physics of light-matter interactions.

Primary authors and contact information:

• Tobias Zier – tzier2@ucmerced.edu
• David A. Strubbe – dstrubbe@ucmerced.edu

DOI: 10.1038/s42005-025-02238-3