An international team has managed to capture an elusive state of matter that stays stable even at room temperature. It's called a supercrystal, and all it took was laser pulses shorter than a blink of the eye
Okay, so of course it's more complicated than that. The experiment involved layering of anorganic compounds and "frustrating" them, which meant building a structure that prevents the materials from naturally achieving their 'preferred' state of crystallisation
As the frustrated materials were hovering in a disorganized manner, a special laser technique
"We are looking for hidden states of matter by taking the matter out of its comfortable state, which we call the ground state," said materials scientist Venkatraman Gopalan of Penn State
"We do this by exciting the electrons into a higher state using a photon, and then watching as the material falls back to its normal state." The idea is that in an excited state, or in a state it passes through the blink of an eye on the way to the ground state, we will find properties that we would like to have, such as new forms of polar, magnetic and electronic states. "
not make supercrystals out of any old matter. The team used alternating layers of single-atom thick titanate titanate and strontium titanate, stacked into a three-dimensional structure. They grew these layers on a base of dysprosium scandium oxide, whose crystals are between the two crystals formed by the two other materials.
This unique build has let the researchers achieve the frustration we mentioned earlier.
Lead titanate is ferroelectric, a material that has positive and negative electric poles. Strontium titanate is not ferroelectric, and as these materials have been stacked, the electric polarization vectors have to contort into weird pathways, curving back to themselves to create vortices
The size of the crystals in the base provided the last necessity: strontium titanate tried to stretch it to match the size of the substrate's crystals, and lead titanate tried to compress. The result is a particularly disorganized, frustrated system, with multiple states distributed throughout the material.
The team then used what they call a "pump-probe" laser technique. A femtosecond pulse of blue laser "light" is lightning-like, on the structure, which excites the electrons. This is followed by the "probe" light, a more gentle pulse that reads the state of matter.
They found that, rather than slipping back into its disordered state, as could be expected, the matter was trapped in an intermediate supercrystal state indefinitely ̵
"By virtue of its short pulse duration, an ultrafast laser imprints the excitations in materials faster than their intrinsic response time," said scientist Vlad Stoica of the Penn State and Argonne National Laboratory
. "While such dynamic transformations were already
A supercrystal typically has abnormally large unit cells – the smallest repeating unit in a crystal's three-dimensional structure
The supercrystal achieved in this study had unit cells with a volume of at least a million times greater than the unit cells of lead titanate and strontium titanate, all organized as soldiers in formation. ] In room temperature, this formation remained stable for at least a year, and could potentially stay stable indefinitely.
"For the first time, we have observed that as "This experimental demonstration has already stimulated the theoretical developments and has important implications toward the development of the artefacts, "
The research has been published in Nature Materials .