Understanding superconductivity in all its forms has for decades been among scientists’ most prized ambitions. If we could ascertain why some materials, under certain conditions, lose their electrical resistance, we would be closer to the dream of far more efficient and environmentally friendly power grids. Further, superconducting materials are a valuable raw material input for the emerging quantum technology. The 26th Nicolás Cabrera International Summer School brings together leading specialists in “high-temperature superconductivity,” right now the holy grail for dozens of laboratories all around the world.
6 September, 2019
The School, supported by the BBVA Foundation, will be held in the La Cristalera residence in Miraflores de la Sierra from 8 to 13 September. This year’s edition takes as its title “Driving the Road towards Room Temperature Superconductivity with Electronic Interactions,” and will welcome some 70 participants from thirteen different countries.
“The goal of the School is to have leading figures in high-temperature superconductivity present the state of the art in this vibrant area,” the organizers explain. “World-class experts will discuss where research is currently headed, focusing on the latest developments, both theoretical and experimental.”
This edition of the School is organized by Isabel Guillamón, a Ramón y Cajal Fellow at the Universidad Autónoma de Madrid (UAM), who followed up her receipt of a BBVA Foundation Leonardo Grant by winning a prestigious Starting Grant from the European Research Council; Elena Bascones, a tenured scientist at the Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC); and Hermann Suderow, head of the Nicolas Cabrera Institute since 2012.
Electrons that travel better in pairs
Not a week goes by without some top scientific journal publishing a major new finding in high-temperature superconductivity, giving some idea of how active this area is. To understand these advances, we must first pay a visit to the quantum world and learn about the strange behavior of electrons.
Superconductivity was discovered more or less by accident in 1911. Its discoverer, the Dutch scientist Heike Kamerlingh-Onnes, quickly saw its potential for transmitting electrical power without energy losses. The problem was that superconductivity only emerged when materials were cooled to a few degrees above absolute zero, -273ºC.
The first theoretical breakthrough was the explanation of how superconductivity comes about. In 1957, three researchers concluded that when certain materials are cooled to near absolute zero, their electrons form pairs which can then advance freely past any obstacle.
By the late 1980s, the intense search for superconducting materials at higher temperatures had yielded its first results. Certain cuprate ceramics (copper oxide compounds) were found to become superconducting at “just” -180ºC. Though still very low, these were significantly more manageable temperatures, in that they could be reached using liquid nitrogen instead of the far costlier liquid helium.
A further milestone came in 2008 with the discovery of new high-temperature superconductors, iron-based this time. The race for high-temperature superconductivity picked up once again. Currently the record temperature at which a material turns superconducting is still far from what we might call room temperature, but there is nothing in the theory to say that the dream of superconductivity at 20ºC is beyond reach.
Searching in the dark
Yet this remains very much a blind search, since the phenomenon itself is poorly understood. Electron pairs continue to be formed in high-temperature superconductivity, but we have little idea why. “High-temperature superconductivity, the kind with most applicability, is still an enigma,” the organizers remark.
“Researchers set themselves the goal of finding superconductors at really high critical temperatures in the late 1980s, after cuprate superconductivity came to light. And after thirty years’ effort they have gained a new focus with the discovery of iron-based superconducting compounds.”
In the meantime, superconductivity has not been without its practical applications, some of which have enabled crucial advances in science and medicine. The magnets of particle accelerators like the large hadron collider (LHC) at CERN, where the Higgs boson was detected, are superconductors; and they are also used in magnetic resonance (NMR) scanners, generators, telecommunications devices and magnetic levitation trains. Not only that, some superconducting power cables are already operating on a test basis. The first was installed on Long Island, New York, in 2008 and now serves 300,000 homes.
But applications would likely multiply if the phenomenon was better understood. To start with, no electricity would be lost in its journey through the grid, because “high-tension pylons could be replaced by underground ‘pipelines’ that would suffer no losses whatsoever,” the organizers explain, “thereby eliminating their environmental impact and improving distribution efficiency.”
Also, while superconducting materials are considered vital for the development of quantum computing, their low temperature is a limiting factor – one more reason to seek out higher-temperature superconducting materials.
Among those present at the School will be Irish physicist Seamus Davis, a professor at Cornell University (United States), University College Cork (Ireland), and the University of Oxford (United Kingdom) and author of created one of the most powerful techniques for visualizing the behavior of electrons in quantum materials. Davis is also co-author of some of the recent papers of most impact in superconductivity.
Also attending will be Spain’s Pablo Jarillo-Herrero (Valencia, 1976), Cecil and Ida Green Professor of Physics at Massachusetts Institute of Technology (MIT), who in 2012 won the U.S. Government’s foremost distinction for young researchers, the Presidential Early Career Award for Scientists and Engineers, funded with one million dollars, which he plowed back into his research.
Last year Jarillo caused a stir in the area by discovering that graphene becomes a superconductor if one of two sheets of the material – each a single atom thick – is placed on top of the other and rotated to form what has become known as the “magic angle” of 1.1 degrees. Although the reason for this phenomenon is not yet known, there is strong evidence that its study will contribute to a deeper understanding of high-temperature superconductivity.
Teresa Puig Molina, head of the Department of Superconducting Materials and Large-Scale Nanostructures at the Instituto de Ciencia de Materiales de Barcelona (ICMAB-CSIC), is exploring ways to scale the production of high-temperature superconducting materials so they are competitive vs conventional metal conductors.
Her group has received a Proof of Concept Grant from the European Research Council to develop industrial and economically viable processes for forming ultrathin layers of superconducting material on a flexible support.
Other speakers include Francisco Guinea, Research Professor at the Instituto de Ciencia de Materiales de Madrid (ICMMM-CSIC) and winner of the 2011 National Research Prize for his internationally acclaimed work, especially on graphene; and Swedish physicist Annica Black-Schaffer of Uppsala University, widely recognized for her research into superconducting materials and their applications in quantum computing.