Some materials can transmit signals without conducting electricity or losing energy. Theoretical physicist Rembert Duine studies this principle, and has recently received the prestigious ERC Consolidator Grant worth more than 1.5 million Euros to facilitate his work. He will use the grant to better understand conduction by means of so-called ‘spin waves’, a quantum mechanical characteristic of electrons that is the foundation of this new, energy-efficient alternative means of transferring information.
“Electrical conduction always involves an irreversible loss of energy”, Duine begins. “Electrons flow from point A to point B, and occasionally they bump into one another or into irregularities in the material - especially at room temperature. This creates heat, which is a loss of energy.” In addition to having an electrical charge, electrons also have what is known as a ‘spin’: an abstract concept that is comparable to a built-in compass needle, and which is the basis of the material’s magnetic characteristics. Sometimes, all of the compass needles point in the same direction, but under the influence of a magnetic field, a wave-like motion may occur.
These waves can also be a means of transporting information, in theory without a loss of energy. Duine: “The electrons themselves do not move; instead, they form a series of waving compass needles. And since they don’t move, they cannot collide. With this method, it may be possible to make the equivalent of a superconductor”, he envisions, then immediately cautions: “The physics behind this is still in its infancy: there is still a lot about this principle that we don’t understand.”
Duine looks for the yet-unanswered questions in the field of quantum mechanics. He and the PhD candidates in his research group perform the many calculations using computers, but more often with simple pen and paper, to use theoretical models to predict the behaviour of the spin in various materials. Duine studied and earned his PhD in Utrecht, and after a postdoc at the University of Texas he went to work at the Institute for Theoretical Physics. There, he received some major subsidies for his work, including a VIDI grant from NWO and an ERC Starting Grant.
In 2015, Duine participated in an experiment in which a spin signal was transmitted over an isolator for the first time. This non-conductive material, a layer of yttrium-iron granulate flanked by two strips of platinum, appeared to conduct a measurable ‘electric’ current created by a spin wave.
“I do a lot of work together with research groups that conduct experimental work”, says Duine, who is also a part-time Professor at TU Eindhoven. Together they look for new materials to utilise these spin waves.
Re-utilising residual heat
The spin of electrons is already used to store information on hard drives, but a potential new use may be the re-utilisation of residual heat. Duine: “Spin waves may make it possible to convert heat into electrical energy. This would require the development of materials with the right thermo-electric characteristics, however. If we can find those materials, and we can re-utilise even just a few percent of that residual heat, then we will be able to generate as much energy as that produced by all of the solar and wind energy combined. We’re still a long way from that point, but it is an indication of the potential presented by spin waves.”