Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


A Grand Unified Theory of Exotic Superconductivity?

Scientists introduce a general theoretical approach that describes all known forms of high-temperature superconductivity and their "intertwined" phases

Years of experiments on various types of high-temperature (high-Tc) superconductors—materials that offer hope for energy-saving applications such as zero-loss electrical power lines—have turned up an amazing array of complex behaviors among the electrons that in some instances pair up to carry current with no resistance, and in others stop the flow of current in its tracks.

The variety of these exotic electronic phenomena is a key reason it has been so hard to identify unifying concepts to explain why high-Tc superconductivity occurs in these promising materials.

Now Séamus Davis, a physicist who's conducted experiments on many of these materials at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Cornell University, and Dung-Hai Lee, a theorist at DOE's Lawrence Berkeley National Laboratory and the University of California, Berkeley, postulate a set of key principles for understanding the superconductivity and the variety of "intertwined" electronic phenomena that applies to all the families of high-Tc superconductors. They describe these general concepts in a paper published in the Proceedings of the National Academy of Sciences October 10, 2013.

"If we are right, this is kind of the 'light at the end of the tunnel' point," said Davis. "After decades of wondering which are the key things we need to understand high-Tc superconductivity and which are the peripheral things, we think we have identified what the essential elements are."

Said Lee, "The next step is to be able to predict which other materials will have these essential elements that will drive high Tc superconductivity—and that ability is still under development."

The role of magnetism

In all known types of high-Tc superconductors—copper-based (cuprate), iron-based, and so-called heavy fermion compounds—superconductivity emerges from the "extinction" of antiferromagnetism, the ordered arrangement of electrons on adjacent atoms having anti-aligned spin directions. Electrons arrayed like tiny magnets in this alternating spin pattern are at their lowest energy state, but this antiferromagnetic order is not beneficial to superconductivity.

However if the interactions between electrons that cause antiferromagnetic order can be maintained while the actual order itself is prevented, then superconductivity can appear. "In this situation, whenever one electron approaches another electron, it tries to anti-align its magnetic state," Davis said. Even if the electrons never achieve antiferromagnetic order, these antiferromagnetic interactions exert the dominant influence on the behavior of the material. "This antiferromagnetic influence is universal across all these types of materials," Davis said.

Many scientists have proposed that these antiferromagnetic interactions play a role in the ability of electrons to eventually pair up with anti-aligned spins—a condition necessary for them to carry current with no resistance. The complicating factor has been the existence of many different types of "intertwined" electronic phases that also emerge in the different types of high-Tc superconductors—sometimes appearing to compete with superconductivity and sometimes coexisting with it.

Intertwined phases

In the cuprates, for example, regions of antiferromagnetic alignment can alternate with "holes" (vacancies formerly occupied by electrons), giving these materials a "striped" pattern of charge density waves. In some instances this striped phase can be disrupted by another phase that results in distortions of the stripes. In iron-based superconductors, Davis' experiments revealed a nematic liquid-crystal-like phase. And in the heavy fermion superconductors, other exotic electronic states occur.

"When so many intertwined phases were discovered in the cuprates, I was strongly discouraged because I thought, 'How are we going to understand all these phases?'" said Lee. But after the discovery of the iron-based superconductors about five years ago, and their similarities with the cuprates, Lee began to believe there must be some common factor. "Séamus was thinking along a similar line experimentally," he said.

In the current paper, Davis and Lee propose and demonstrate within a simple model that antiferromagnetic electron interactions can drive both superconductivity and the various intertwined phases across different families of high-Tc superconductors. These intertwined phases and the emergence of superconductivity, they say, can be explained by how the antiferromagnetic influence interacts with another variable in their theoretical description, namely the "Fermi surface topology."

"The Fermi surface is a property of all metals and provides a 'fingerprint' of the specific arrangements of electrons that are free to move that is characteristic of each compound," Davis said. "It is controlled by how many electrons are in the crystal, and by the symmetry of the crystal, among other things, so it is quite different in different materials."

The theory developed by Lee incorporates the overarching antiferromagnetic electron interactions and the known differences in Fermi surface from material to material. Using calculations to "dial up" the strength of the magnetic interactions or vary the Fermi surface characteristics, the theory can predict the types of electronic phases that should emerge up to and including the superconductivity for all those different conditions.

"The basic assumption of our theory is that when we rip away all the complicated intertwined phases, underneath there is an ordinary metal," said Lee. "It is the antiferromagnetic interactions in this metal that make the electrons want to form the various states. The complex behavior originates from the system fluctuating from one state to another, e.g., from superconductor to charge density waves to nematic order. It is the antiferromagnetic interaction acting on the underlying simple metal that causes all the complexity."

"So far this theory has correctly produced all the electronic phases that we have observed in each type of strongly correlated superconductor," Davis said.

The next step is to search through new materials and use the theory to identify which should operate in similar ways—and then put them to the test to see if they follow the predictions.

"It is one thing to say, 'If we have the key ingredients, then a material is likely to exhibit high Tc superconductivity.' It is quite another thing to know which materials will have these key characteristics,'" Lee said.

If the search pays off, it could lead to the identification or development of superconductors that can be used even more effectively than those that are known today—potentially transforming our energy landscape.

This research was funded by the DOE Office of Science, in part through the Center for Emergent Superconductivity, a DOE-funded Energy Frontier Research Center at Brookhaven National Laboratory.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit

Karen McNulty Walsh | EurekAlert!
Further information:

More articles from Materials Sciences:

nachricht Scientists have a new way to gauge the growth of nanowires
19.03.2018 | DOE/Argonne National Laboratory

nachricht Researchers demonstrate existence of new form of electronic matter
15.03.2018 | University of Illinois at Urbana-Champaign

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

Physicists made crystal lattice from polaritons

20.03.2018 | Physics and Astronomy

Mars' oceans formed early, possibly aided by massive volcanic eruptions

20.03.2018 | Physics and Astronomy

Thawing permafrost produces more methane than expected

20.03.2018 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>