Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS


SUPERBAD Berichtzusammenfassung

Project ID: 240524
Gefördert unter: FP7-IDEAS-ERC
Land: Italy

Final Report Summary - SUPERBAD (Understanding high-temperature superconductivity from the foundations: Superconductivity as a cure of bad metallic behaviour)

The overarching idea of the SUPERBAD project is to understand why the highest superconducting critical temperatures (in other words, the best superconductors) are not obtained in ideal conductors, but rather in very bad metals arising by chemically doping the so-called Mott insulators, materials in which the repulsive interaction between the electrons is so strong to completely inhibit the motion of the carriers.

As a matter of fact superconductivity, which arises from attractive interactions binding the electrons in Cooper pairs, surprisingly finds its most spectacular realization in materials dominated by repulsion.

SUPERBAD finds a solution to this puzzles identifying high-temperature superconductivity as a “cure” for the bad metallic behavior determined by the repulsive interactions, and aims to exploit this event to reveal how to increase the superconducting critical temperature in new materials.

The role of electronic correlation induced by the strong interactions is widely recognized for the most known high-temperature superconductors, copper-oxides (cuprates) which reach critical temperatures of around 140K, but the recent years have witnessed the discovery of several other superconducting materials with reasonably high critical temperatures and with interesting and peculiar properties. Among these a family of compounds based on iron and molecular solids composed of football-like fullerene molecules.

Within the SUPERBAD project we have identified a common origin of high-temperature superconductivity in the cuprates, iron-based superconductors and fullerenes and proposed a general recipe to design a high-temperature superconductor.

A crucial step towards a unified theory of all these superconductors is a fascinating analogy between the iron-based superconductors and the cuprates, based once again on the proximity to a strongly correlated Mott state. This is rather surprising because in the iron-based family the parent compounds which turn superconducting under doping are not “Mott insulators” but metallic metals. The analogy between the two families is based on the idea that the iron-based materials can be described as the result of doping a virtual Mott insulator which would be realized if we could dope one hole every iron site.

Finally, SUPERBAD has focused on the properties of superconductors brought out of equilibrium by a laser pulse. Following, as in a motion picture, the time evolution of the system after the laser excitation, we can disentangle different physical phenomena that are strongly intertwined in equilibrium gaining fundamental information about the origin of superconductivity.

The route towards an improved understanding of high-temperature superconductors requires the development of specific theoretical “tools” designed to obtain a reliable and quantitative description of superconductivity in correlated materials. Within SUPERBAD we developed a theoretical approach which merges two popular approaches (Dynamical Mean-Field Theory and Density-Functional Theory) to describe strongly correlated superconductivity in a realistic framework and we have been able to reproduce the phase diagram of fullerene superconductors using simply the information about the crystal structure. This approach will be used in the near future to predict structures of novel superconductors with our computers.

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