Teams from the Johannes Gutenberg University Mainz (JGU) in Germany and Stanford University have uncovered a new quantum state of matter in Heusler compounds which they claim opens up 'previously unimagined usage possibilities'. The scientist from Mainz has shown that many Heusler compounds can behave like topological insulators (TI).

TIs have been studied in the field of solid state and material physics. Characteristic of topological insulators is the fact that the materials are actually insulators or semiconductors, although their surfaces or interfaces are made from metal - but not ordinary metal. Like superconductors, the electrons on the surfaces or interfaces do not interact with their environment - they are in a new quantum state. In contrast with superconductors, topological insulators have two non-interacting currents, one for each spin direction. These two spin currents, which are not affected by defects or impurities in the material, can be employed in the futuristic electronics field of 'spintronics' and for processing information in quantum computers.

It is now supposed that Heusler materials may have the same capabilities. Heusler compounds are made up of three elements, which often have semiconductor or magnetic properties. One special feature of these compounds is that they exhibit characteristics other than those that might be expected in view of the elements of which they are composed. The first Heusler compound, for example, was made from the non-magnetic elements copper, manganese, and aluminium. Yet, Cu2MnAl acts as a ferromagnet, even at room temperature. On the other hand, a semiconductor can result when three metals are combined. New semiconductors can be designed in the class of Heusler materials with regard to the field of renewable energies; they can be used in solar cells or in thermoelectric applications, for converting heat into electricity. Important discoveries with regard to Heusler compounds, their properties and uses in a range of potential applications have been made in Mainz.

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