Researchers reveal the fourth signature of the superconducting transition in cuprates

35 years ago, researchers cheered when an exciting and unconventional new class of materials was discovered.

When copper oxides or cuprates are chilled below a certain point, they conduct electricity with no resistance or loss, but at much higher temperatures than scientists had thought possible. They were hoping to be able to work at close to room temperature for efficient power lines and other uses.

As superconductivity developed, the material expelled magnetic fields, so that a magnet placed on a chunk of the material would levitate above the surface. The amount of heat needed to raise their temperature by a given amount was atypical at the transition.

The fourth signature, the way electrons pair up and condense into a soup as the material transitions from its normal state to a superconducting state, remained elusive despite decades of effort with a variety of experimental tools.

The fourth signature with precise, high-resolution measurements made with angle-resolved photoemission spectroscopy, or ARPES, has been revealed by a research team at the Department of Energy. The electrons inside the material behave differently when measured.

In a paper published today in Nature, the team confirmed that the material they studied, known as Bi2212, made the transition to a superconducting state in two distinct steps and at very different temperatures.

Sudi Chen, the leader of the study, said that they can think about how to make the transition happen at higher temperatures.

The culmination of 15 years of scientific detective work in trying to understand the electronic structure of these materials is what Professor Zhi-Xun Shen said. The amazing thing is that it took so long to find it, because we knew these materials should produce distinctive spectroscopic signatures.

There are unconventional transitions.

In conventional superconductors, electrons overcome their mutual repulsion and form what are known as Cooper pairs, which immediately condense into a sort of electron soup that allows electrical current to travel unimpeded.

Scientists theorize that electrons pair up at one temperature but don't condense until they're cooled to a lower temperature, which is when the material becomes superconductivity.

Until now, the details of this transition had been explored with other methods, but not with probes like photoemission spectroscopy that study how matter absorbs light and emits electrons. It is an important measure of how electrons behave.

When the discovery of the new cuprate superconductors was coming to light, he started his scientific career at Stanford and devoted more than three decades to unraveling their secrets.

Cuprate samples made by Japanese partners were examined at two different locations, one in a laboratory with an ultraviolet laser and the other in a lab with a radiation light source.

Peeling a onion.

Recent improvements in the performance of those instruments were an important factor in obtaining these high-quality results.

It is difficult to get a full understanding of the physics of high-temperature superconductivity. Experimentalists use different tools to investigate different aspects of the problem.

The long-term study of these unconventional materials has been like peeling layers from an onion to reveal the surprising and interesting physics within.

He said that the transition to superconductivity occurs in two separate steps and that they can tune the materials to superconduct at higher temperatures.

More information: Zhi-Xun Shen, Unconventional spectral signature of Tc in a pure d-wave superconductor, Nature (2022). DOI: 10.1038/s41586-021-04251-2. Journal information: Nature Citation: Researchers reveal the fourth signature of the superconducting transition in cuprates (2022, January 26) retrieved 26 January 2022 from https://phys.org/news/2022-01-reveal-fourth-signature-superconducting-transition.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.