Researchers from the University of Miami
(UM) are unveiling a novel theory for high-temperature superconductivity. The
team hopes the new finding gives insight into the process, and brings the
scientific community closer to achieving superconductivity at higher temperatures
than currently possible.

Superconductors are composed of specific metals or mixtures
of metals that at very low temperatures allow a current to flow without
resistance. They are used in everything from electric devices, to medical
imaging machines, to wireless communications. Although they have a wide range
of applications, the possibilities are limited by temperature constraints.

“Understanding how superconductivity works at higher
temperatures will make it easier to know how to look for such superconductors,
how to engineer them, and then how to integrate them into new
technologies,” says Josef Ashkenazi, associate professor of physics at the
UM College of Arts and Sciences and first author of
the study. “It’s always been like this when it comes to science: once you
understand it, the technological applications follow.”

At room temperature, superconducting materials behave like
typical metals, but when the temperature is lowered toward absolute zero (at
around -273 C, or -460 F), resistance to electric current suddenly drops to
zero, making it ultra-efficient in terms of energy use. Although absolute zero
is unachievable, substances such as liquid helium and liquid nitrogen can be
used to cool materials to temperatures approaching it.

Researchers are also working on creating materials that
yield superconductivity in a less frigid environment. The point at which a
matter becomes a superconductor is called critical or transition temperature.
So far, the highest critical temperature of a superconducting material is about
-130 C (-200 F).

“But just ‘cooking’ new materials that produce
superconductivity at higher temperatures can be very tedious and expensive,
when one doesn’t know exactly how the process works,” says Neil Johnson,
professor of physics in the UM College of Arts and Sciences and co-author of
the study.

To understand the problem, the UM team studied what happens
in a metal at the exact moment when it stops being a superconductor. “At
that point, there are great fluctuations in the sea of electrons, and the
material jumps back and forth between being a superconductor and not being
one,” Johnson says.

The key to understanding what happens at that critical point
lies in the unique world of quantum particles. In this diminutive universe,
matter behaves in ways that are impossible to replicate in the macroscopic
world. It is governed not by the laws of classical physics, but by the laws of
quantum mechanics.

One of the most perplexing features of quantum mechanics is
that a system can be described by the combination or ‘superposition’ of many
possible states, with each possible state being present in the system at the
same time. Raising the critical temperature of superconductors is prevented in
common cases, because it creates a fragmentation of the system into separate
states; this act suppresses high-temperature superconductivity.

What Ashkenazi and Johnson found is that just above the critical
temperature specific quantum effects can come to the floor and generate
superpositions of individual states. This superposition of states provides an
effective “glue,” which helps repair the system, allowing
superconducting behavior to emerge once again. This model provides a mechanism
for high temperature superconductivity.

“Finding a path to high-temperature superconductivity
is currently one of the most challenging problems in physics,” says
Ashkenazi. “We present for the first time, a unified approach to this
problem by combining what has prevented scientists from achieving
high-temperature superconductivity in the past, with what we now know is
permitted under the quantum laws of nature.”

“The new model combines elements at two levels:
physically pulling together the fragments of the system at the quantum level,
and theoretically threading together components of many other existing theories
about superconductivity,” Johnson says.

Understanding how superconductivity is pushed beyond the
present critical temperatures will help researchers recreate the phenomenon at
a wider temperature range, in different materials, and could spur the
development of smaller, more powerful, and energy-efficient technologies that
would benefit society.

Source: University of Miami