Physicists at the University of Massachusetts Amherst and Sweden's Royal Institute of Technology have published what they claim is a self-consistent theory of Type 1.5 superconduction.
Type 1.5 is a newly-proposed state, possible in a class of materials called multi-band superconductors.
"For years, most physicists believed that superconductors must be either Type I or Type II," said the University of Massachusetts. "Type 1.5 is the subject of intense debate because until now there was no theory to connect the physics with the micro-scale properties of real materials."
There is now a theoretical framework to allow scientists to calculate conditions necessary for the appearance of Type 1.5 superconductivity, which exhibits characteristics of Types I and II.
Charge flow patterns are different in Type I and Type II, and were thought to be antagonistic.
Discovered in 1911, Type I has two state-defining properties: no electric resistance, and impenetrability to magnetic fields.
When a magnetic field is applied, electrons produce a surface current that makes a magnetic field in the opposite direction. Inside, the fields sum to zero.
Type II superconductivity was predicted by a Russian theoretical physicist who said that there should be materials with a complicated flow of superconducting electrons where a magnetic field can gradually penetrate, carried by electron vortices.
The combined works that theoretically described Type I and II superconductivity won the Nobel Prize in 2003.
The first kind of supercurrent forming vortices.
All super- conducting materials discovered in the last half-century can be classified as either Type I or II, said Egor Babaev, formerly at UMass Amherst, now at Stockholm's technology institute, who foresaw a possible third state where superconducting electrons could be classed as two competing subpopulations, one behaving like electrons in Type I material, the other behaving like electrons in a Type II material.
In these materials, there would be clusters of tightly packed current vortices with some electrons bunched together and others flowing on the surface of vortex clusters in a way similar to those on the exterior of Type I superconductors.
The clusters would be separated by voids with no vortices, currents or magnetic field.
Using supercomputer modelling, conditions were discovered where forces give vortex clusters very complicated structures in which two populations of electrons develop, behaving differently.
The other electron sub- population on the surface of a vortex cluster.
"With the development of theory that works on the microscopic level, as well as our better understanding of inter-vortex interaction, we can now connect the properties of vortex clusters with the properties of electronic structure of concrete materials. This can be useful in establishing whether materials belong in the Type 1.5 superconductivity domain," said Babaev.