A new type of metallic state of matter was discovered by an international team of researchers who were studying a superconductor made with carbon 60 molecules, fullerenes better known as buckyballs.
The team found the new state after changing the distance between the adjacent C60 molecules sticking rubidium atoms between them.
The analysis of the material revealed a rich combination of insulating phases, magnetic, metal, and even more interesting, superconducting - including state hitherto unknown, which was called "Jahn-Teller metal".
The Jahn-Teller effect (described by Hermann Arthur Jahn and Edward Teller) is characterized by deformation of the crystal lattice geometry of a material when orbital states of molecules are subdivided to reduce system power.
Low pressure, the material studied by the team is an insulator, whereupon the electronic state of the molecules is distorted by the Jahn-Teller effect. As pressure is applied by the addition of rubidium, the electronic states of the molecules begin to overlap, and the material undergoes a "Mott transition" to become a simple metal.
It is in the middle of this insulator-metal transition that appeared intermediate never before been seen, which is marked by a change in shape of the C60 molecules, which become elongated.
And this is a key point in understanding the superconductivity because it is the metallic phase which becomes superconducting when the material is taken below a critical temperature.
The study provides important clues on how the interaction between the electronic structure of molecules and their spacing within the crystalline material network can strengthen the interactions between the electrons that cause superconductivity.
Superconductors are a large and diverse group of materials that offer zero resistance to the passage of electrical currents when cooled below a critical temperature. Although superconductivity involves electrons form pairs, called Cooper pairs, the mechanism by which this occurs is not fully understood in all types of superconductors - especially in the superconducting considered "high temperature".
The expectation is that knowledge of this new phase can result in the development of new molecular materials that become superconducting at higher temperatures.