Researchers from Brown University and the University of Michigan have pulled off a trick that was previously confined to the fever dreams of theoretical physicists: they created and stabilized a new phase of matter using tiny silver particles arranged like cosmic LEGO bricks. The work, published in the journal Science, captures an intermediate structural state that flashes into existence during the transformation between two common crystal arrangements found in metals - a state so fleeting that scientists had only guessed it existed.
The newly minted material doesn't just sit there looking exotic; it also displays unusual optical behavior, specifically deep-strong light-matter coupling, where electrons inside the silver nanoparticles vibrate in lockstep with light waves and become quantum mechanically entangled. Remarkably, this effect occurs at room temperature, which is like finding a penguin thriving in the Sahara. The researchers suggest this could eventually be useful for quantum computing and other quantum information technologies - because what the world needs is more ways to compute things that are simultaneously here and not here.
To build their microscopic marvel, the team synthesized silver nanoparticles shaped like truncated octahedra - they call them "mecons" - which resemble a diamond with its corners lopped off, resulting in a 14-sided geometry. Lead author Yasutaka Nagaoka and the team adjusted heating conditions to produce mecons with varying degrees of roundness, then coated them with long molecular chains that acted like sticky connectors, allowing the particles to self-assemble into larger ordered structures called nanoparticle superlattices.
"Our work is a little bit like kids playing with LEGO blocks," said Ou Chen, an associate professor of chemistry at Brown and a corresponding author, in what may be the most relatable scientific analogy since "it's like a balloon and a brick." The molecular coatings, the team found, played a critical role in stabilizing arrangements that matched the transitional structures predicted by the Nishiyama-Wassermann pathway - a leading model for how metals shift between face-centered cubic (FCC) and body-centered cubic (BCC) crystal arrangements.
"Materials scientists have cared about how to control the amount of FCC and BCC in their metals for a long time, but the transitions between these phases have been hard to study because they are so unstable," said Tim Moore, a study co-author from the University of Michigan. "Being able to observe these structures is a fundamental breakthrough in materials science." The research was supported by a small mountain of grants from the National Science Foundation and the Department of Energy, because apparently discovering a new phase of matter isn't cheap.
"Anytime you're able to identify a new phase of matter, new applications are going to emerge," Chen added, which is the scientific equivalent of "build it and they will come" - assuming "they" are quantum computers and advanced sensors.