Material lets magnetic fields move like electrons

The quantum phenomena of materials are often very difficult to investigate due to the extremely small scale at which they take place and the sensitivity for defects in the materials. Researchers have now managed to develop a system with which you can study these phenomena at a far larger scale. They created a material that contains 90,000 small islands of the element niobium and each of these islands behaves like an artificial atom. These islands are about 200 nanometres in size and lie about 50 nanometres from each other (a nanometre is 1 million times smaller than a millimetre). The system is therefore very small but compared with the world of real atoms and electrons it is gigantic. If you apply an external magnetic field above these islands then tiny magnetic fields arise between the islands with a fixed, quantised size. 

Artificial atoms and electrons
As the magnetic fields behave like artificial electrons and the islands can be viewed as artificial atoms, the material can be used to accurately investigate the relationship between the grid of atoms and the behaviour of the electrons at a relatively large scale. The research therefore bridges the gap between the world of classical mechanics and that of quantum mechanics.

Sliding puzzle
The research specifically examined the so-called Mott transition of an insulating state to a conducting state. In an insulator the electrons are trapped. FOM workgroup leader Hans Hilgenkamp, one of the researchers involved, compares this to a sliding puzzle in which the pieces cannot be moved because there are no empty spaces. "If you remove several of the pieces then suddenly all of the puzzle pieces can be shifted along. If you translate that to the world of electrons then a material suddenly becomes conducting."

Melting magnet ice
"In our research we are doing the same with magnetic fields," continues Hilgenkamp. "In our material the magnetic fields are frozen; they sit trapped between the artificial atoms. If we now allow an electric current to flow through the system or we slightly adjust the magnetic field applied then we can remove the frozen state; we melt 'magnet ice' so to speak and magnetic fields can then move in relation to the grid of superconducting islands." The material offers the opportunity to carefully study the transition from insulator to conductor. An important advantage of the material is that you can now investigate this phase transition with a relatively large system. This means you can make far more accurate measurements and can apply a wide range of variations. According to Alexander Brinkman, who was also involved in the research, the team has opened up a new field of research and with this material they have given this field a valuable tool. "We can now use a classical system to study quantum properties at an atomic level. This could, for example, lead to new electronic switches with special types of transistors." 

Research
The research has been published in the journal Science. The research team from the University of Twente consisted of the postdocs Nicola Poccia, Francesco Coneri and Xiao Renshaw Wang, PhD researcher Cor Molenaar and professors Alexander Brinkman, Alexander Golubov and Hans Hilgenkamp. They worked together with scientists from Argonne National Laboratory (US), the Russian Academy of Sciences, the International Center for Materials Science Superstripes in Rome, Novosibirsk State University, the Moscow Institute of Physics and Technology, and the Queen Mary University of London. The research was partly funded by NWO and FOM.