Madrid, 24 years old (European Press)
Such evidence, presented in a paper published in the journal Science, comes from measurements of quantum charge fluctuations known as “shot noise.”
“Noise is significantly suppressed compared to regular cables,” Doug Natelson, study author and scientist at Rice University, said in a statement. “Maybe this is evidence that quasiparticles are not well-defined things or don’t exist and charges move in more complex ways. We have to find the right vocabulary to talk about how charges move collectively.”
Experiments were performed on nanowires of a well-studied quantum critical material with a 1-2-2 min ratio of ytterbium, rhodium and silicon (YbRh2Si2). The material has a high degree of quantum entanglement that produces temperature-dependent behavior.
If it is cooled below a critical temperature, for example, the material instantly switches from a non-magnetic state to a magnetic state. At temperatures just above the critical threshold, YbRh2Si2 is a “heavy fermionic” metal, with charge-carrying quasiparticles that are hundreds of times more massive than bare electrons.
In metals, each quasiparticle, or discrete unit, of charge is the product of countless small interactions between countless electrons. A quasiparticle, first proposed 67 years ago, is a concept physicists use to represent the combined effect of those interactions as a single quantum object for the purposes of quantum mechanical calculations.
Some previous theoretical studies have suggested that the exotic metallic charge carriers may not be quasiparticles, and experiments on gunshot noise have allowed Natelson, the study’s lead author, and Liang Chen, a former student in Natelson’s lab, and more than a dozen Rice co-authors. and the Technical University of Vienna (TU-Wien) to collect the first direct experimental evidence to test the idea.
“Measuring the noise of the shot is basically a way to see how much the charge grains when it passes through something,” said Natelson, a professor of physics, astronomy, electrical and computer engineering, materials science and nanoengineering.
“The idea is that if I’m driving a current, it’s made up of a bunch of separate charge carriers. These get to an average speed, but sometimes they’re closer in time and other times they’re farther apart.”
