A 'breath of nothing' provides a new perspective on superconductivity

July 06, 2020

Zero electrical resistance at room temperature? A material with this property, i.e. a room temperature superconductor, could revolutionize power distribution. But so far, the origin of superconductivity at high temperature is only incompletely understood. Scientists from Universität Hamburg and the Cluster of Excellence "CUI: Advanced Imaging of Matter" have succeeded in observing strong evidence of superfluidity in a central model system, a two-dimensional gas cloud for the first time. The scientists report on their experiments in the renowned journal "Science", which allow to investigate key issues of high-temperature superconductivity in a very well-controlled model system.

There are things that aren't supposed to happen. For example, water cannot flow from one glass to another through the glass wall. Surprisingly, quantum mechanics allows this, provided the barrier between the two liquids is thin enough. Due to the quantum mechanical tunneling effect, particles can penetrate the barrier, even if the barrier is higher than the level of the liquids. Even more remarkably, this current can even flow when the level on both sides is the same or the current must flow slightly uphill. For this, however, the fluids on both sides must be superfluids, i.e. they must be able to flow around obstacles without friction.

This striking phenomenon was predicted by Brian Josephson during his doctoral thesis, and it is of such fundamental importance that he was awarded the Nobel Prize for it. The current is driven only by the wave nature of the superfluids and can, among other things, ensure that the superfluid begins to oscillate back and forth between the two sides - a phenomenon known as Josephson oscillations.

The Josephson effect was first observed in 1962 between two superconductors. In the experiment - in direct analogy to the water flow without level difference - an electric current could flow through a tunnel contact without an applied voltage. With this discovery, an impressive proof had been provided that the wave nature of matter in superconductors can be observed even at the macroscopic level.

Now, for the first time, the scientists in Prof. Henning Moritz's group have succeeded in observing Josephson oscillations in a two-dimensional (2D) Fermi gas. These Fermi gases consist of a "breath of nothing", namely a gas cloud of only a few thousand atoms. If they are cooled to a few millionth of a degree above absolute zero, they become superfluid. They can now be used to study superfluids in which the particles interact strongly with each other and live in only two dimensions - a combination that seems to be central to high-temperature superconductivity, but which is still only incompletely understood.

"We were amazed at how clearly the Josephson oscillations were visible in our experiment. This is clear evidence of phase coherence in our ultracold 2D Fermi gas," says first author Niclas Luick. "The high degree of control we have over our system has also allowed us to measure the critical current above which the superfluidity breaks down."

"This breakthrough opens up many new opportunities for us to gain insights into the nature of strongly correlated 2D superfluids", says Prof. Moritz, "These are of outstanding importance in modern physics, but very difficult to simulate theoretically. We are pleased to contribute to a better understanding of these quantum systems with our experiment."
-end-
Reference

Niclas Luick, Lennart Sobirey, Markus Bohlen, Vijay Pal Singh, Ludwig Mathey, Thomas Lompe, Henning Moritz An ideal Josephson junction in an ultracold two-dimensional Fermi gas Science (2020) DOI: 10.1126/science.aaz2342

University of Hamburg

Related Superconductivity Articles from Brightsurf:

New kind of superconductivity discovered
Superconductivity is a phenomenon where an electric circuit loses its resistance and becomes extremely efficient under certain conditions.

Room temperature superconductivity creeping toward possibility
The possibility of achieving room temperature superconductivity took a tiny step forward with a recent discovery by a team of Penn State physicists and materials scientists.

A 'breath of nothing' provides a new perspective on superconductivity
Zero electrical resistance at room temperature? A material with this property, i.e. a room temperature superconductor, could revolutionize power distribution.

New Princeton study takes superconductivity to the edge
The existence of superconducting currents, or supercurrents, along the exterior of a superconductor, has been surprisingly hard to find.

Superconductivity: It's hydrogen's fault
Last summer, it was discovered that there are promising superconductors in a special class of materials, the so-called nickelates.

How a magnet could help boost understanding of superconductivity
Physicists have unraveled a mystery behind the strange behavior of electrons in a ferromagnet, a finding that could eventually help develop high temperature superconductivity.

New study explains why superconductivity takes place in graphene
Theoretical physicists take important step in development of high temperature superconductors.

Better studying superconductivity in single-layer graphene
A new study published in EPJ B demonstrates that an existing technique is better suited for probing superconductivity in pure, single-layer graphene than previously thought.

Stressing metallic material controls superconductivity
No strain, no gain -- that's the credo for Cornell researchers who have helped find a way to control superconductivity in a metallic material by stressing and deforming it.

First report of superconductivity in a nickel oxide material
Scientists at SLAC and Stanford have made the first nickel oxide material that shows clear signs of superconductivity - the ability to transmit electrical current with no loss.

Read More: Superconductivity News and Superconductivity Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.