Image credit: Yang et al
Strange metals, also known as non-Fermi liquids, are a class of materials that don’t follow traditional electrical rules.
Its behavior was first discovered about 30 years ago in materials called cuprates.
These copper oxide materials are best known as high-temperature superconductors; they conduct electricity with 0 resistance at much higher temperatures than normal superconductors.
But even at temperatures above the critical temperature for superconductivity, cuprates behave strangely compared to other metals. With increasing temperature, the resistance of cuprates increases strictly linearly.
In normal metals, the resistance increases only up to a certain point and becomes constant at high temperatures according to what is known as the Fermi liquid theory.
Resistance arises when electrons flowing in a metal strike into metal’s vibrating atomic structure, causing them to scatter.
Fermi liquid theory sets maximum rate at which electron scattering can occur. But some weird metals don’t follow Fermi liquid’s rules, and nobody’s sure how they work.
What physicists do know is that the temperature-resistance relationship in weird metals appears to be related to 2 fundamental constants of nature: the Boltzmann constant, which represents the energy generated by random thermal motion & the Planck constant, which is related to the energy of a photon.
“To understand what’s going on inside these strange metals, people have applied mathematical approaches similar to those used to understand black holes,” said Dr. valles
“So there is very fundamental physics happening in these materials.
In recent years, dr. Valles & his colleagues studied electrical activities where the charge carriers are not electrons.
In 1952, the Nobel Laureate Leon Cooper discovered that electrons are team-up in normal superconductors to form Coopers pairs, which can glide through an atomic lattice with 0 resistance.
Despite being made up of 2 electrons, which are fermions, Cooper pairs can act as bosons.
“Fermion & boson systems generally behave very differently. Unlike individual fermions, bosons can share the same quantum state, which means they can move together like water molecules in the ripples of a wave,” said Dr. valles
In 2019, researchers showed that the Bosons Cooper pair can produce metal behaviors, which means that they can perform electricity with some resistance.
This was a surprising finding in itself, as elements of quantum theory suggested that the phenomenon should not be possible.
For this latest research, the scientists wanted to see if the Cooper pair bosonic metals were also strange metals.
They used a Cuprate material called yttrium barium copper oxide patterned with small holes, which induce the copper pair metallic state.
They then cooled-down the material to just above its superconducting temperature to observe changes in its conductivity.
Like fermionic foreign metals, they found a metal cooper pair conductance that is linear with temperature.
“It has been a challenge for theorists to find an explanation for what we see in strange metals,” said Dr. valles
“Our work shows that if you plan to model-charge transport in strange metals, this model must be applied to both fermiones & bosons, although these types of particles follow fundamentally different rules..
The findings published in the journal Nature.
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