Researchers have built nanowires with a precise 1:2:2 ratio of ytterbium, rhodium, and silicon (YbRh2Si2) in a peculiar phase of matter. This phase is called "strange metal", and true to its name the quantum material is exhibiting behaviors that have challenged expectations. One of these is that electricity in this material does not move as a discrete package.
In the cables you have around your house, in your devices, and across cities, electrons carry the electrical energy where it is being requested. But this transmission can happen with any charged particle, and sometimes with something that looks and behaves like a particle but is not: a quasiparticle. If something has a distinct charge and is moving through a conductor, electricity flows.
But measurements of this strange metal hint at more complex behavior. Quasiparticles carrying charge in solids produce something called shot noise. For the YbRh2Si2 nanowires, this noise is much lower than what is produced in gold nanowires, or the theoretical expectation for a system of quasiparticles. The team says that the electricity is moving in a fluid-like motion.
“The shot noise measurement is basically a way of seeing how granular the charge is as it goes through something,” corresponding author Doug Natelson, from Rice University, said in a statement.
“The noise is greatly suppressed compared to ordinary wires. Maybe this is evidence that quasiparticles are not well-defined things or that they’re just not there, and charge moves in more complicated ways. We have to find the right vocabulary to talk about how charge can move collectively.”
The behavior of this material, technically known as a heavy-fermion system, is likely to be found elsewhere. The researchers wonder if there are deeper connections in what electricity flow is like across a wide range of materials. They also question what possible consequences there are, and what applications could be developed if these more fundamental insights are uncovered.
“Sometimes, you kind of feel like nature is telling you something. This ‘strange metallicity’ shows up in many different physical systems, despite the fact that the microscopic, underlying physics is very different. In copper-oxide superconductors, for example, the microscopic physics is very, very different than in the heavy-fermion system we’re looking at,” Natelson said.
“They all seem to have this linear-in-temperature resistivity that’s characteristic of strange metals, and you have to wonder if there is something generic going on that is independent of whatever the microscopic building blocks are inside them.”
The study is published in the journal Science.