A stack of playing cards lies still. You can slide the top card with your finger: that's crude intervention. Or you can blow so that the whole stack momentarily changes shape, but the cards don't scatter. That's roughly how light, in a new experiment, rearranges a crystal of tin selenide (SnSe).
Usually, to change the structure of a solid, you heat it or pass a current through it. Light gets absorbed, energy turns into heat, and atoms vibrate more strongly, as if the cards were shaking from heat. Here, instead, they used an infrared laser pulse so intense that the light's electric field directly yanked the atoms, without time to heat them. The key is that the force arises from the gradient of the dielectric permittivity, the material's ability to polarize, as atoms shift. This resembles an optical tweezer that holds a microscopic bead in the beam's focus: light doesn't heat the bead but pushes it toward the center, where the field is brighter. Only here, light pushes not a bead but entire layers of atoms, forcing them into a new position.
The authors directed mid-infrared pulses at a tin selenide sample and monitored the response using time-resolved Raman scattering. When the power exceeded a threshold, the characteristic lattice vibrations, the so-called $A_g$ modes, vanished abruptly, without prior softening. That's a sign that the crystal entered a new phase, unlike the one produced by heating or charge-carrier pumping. The new phase turned out to be long-lived and showed strong modulations in the optical response. Additionally, using atom-probe tomography, the scientists saw that a static electric field can also induce a structural transition: this time to a phase with higher symmetry.
The discovery means that 'hidden' phases of materials, those not achievable by ordinary heating or pressure, can be synthesized quickly and without excess energy costs. A laser pulse acts as a contactless switch, paving the way for devices where a material's structure changes on command of light. So a stack of cards, obedient to a gentle breath, finds a new order — only now the breath is light, and the order is atomic.
The optical tweezer, invented by Arthur Ashkin in the 1970s, was originally meant for trapping microscopic particles and even living cells. Now the same principle, light pressure without absorption, makes entire crystals change their architecture.
In Arthur C. Clarke's novel 'The Light of Other Days,' light beams control matter at a distance — a similar idea underlies optomechanical phase control, only here light doesn't heat but mechanically pushes atoms.