Electric voltage from quantum mechanical electron spin

Researchers at the Technische Universität Ilmenau have succeeded in using the intrinsic angular momentum of electrons - the so-called electron spin, or spin for short - to generate electric voltage. The measured voltages are still tiny, but the scientists hope that their work will enable them to create high-performance batteries of the future. The research work of the team headed by Prof. Christian Cierpka and Prof. Jörg Schumacher from the Institute of Thermodynamics and Fluid Mechanics has just been published in the renowned journal Physical Review Applied.

The latest generation of laptop and mobile phone memory uses findings from one of the latest research areas in nanoelectronics: spintronics. Today's data density of modern terminals would be impossible without the giant magnetoresistance, a phenomenon based on the collective dynamics of spin, the intrinsic angular momentum of electrons, which was discovered by Peter Grünberg and awarded the Nobel Prize in Physics in 2007. In the work, which has now been accepted for publication by Physical Review Applied, researchers led by Prof. Christian Cierpka and Prof. Jörg Schumacher from the TU Ilmenau investigated another spintronic effect. In a series of experiments, they verified and extended earlier investigations by a Japanese research group from Sendai for the first time: With the help of the collective coupling of the spins to flow vortices, an electrical voltage was generated.

In a tube made of special glass, a capillary with a diameter of less than one millimeter, the scientists generated currents by forcing liquid metal through the tube at several atmospheres of pressure. The electrons in the liquid metal thus formed a kind of gas of freely moving charges, with the electrical voltages measured reaching values of several hundred nanovolts. The voltages were therefore only minutely small, but the Ilmenau scientists are confident that they will be able to generate significantly higher voltages if they optimise the flows so that they cause greater vortex strengths.

The researchers from the Institute for Thermodynamics and Fluid Mechanics are already thinking about the next research steps. How can the tiny tension be increased through geometric effects or nanostructured surfaces? Is it possible to optimize the configuration of the flow vortices in such a way that the collective dynamics of the electron spins is increased? Could the generated electric voltage be increased by connecting several such systems in parallel? At the exciting interface between classical physics and quantum physics, researchers Christian Cierpka and Jörg Schumacher still have to carry out a large number of experiments so that we can one day replace our familiar lithium batteries with "spintronic button cells".

The experiments were carried out as part of the "Experiment! - In Search of Daring Research Ideas" programme, the experiments were funded by the Volkswagen Foundation with 120,000 euros.

Link to the article in Physical Review Applied (Open Access):
journals.aps.org/prapplied/pdf/10.1103/PhysRevApplied.14.014002

Contact:
Prof. Christian Cierpka
Institute for Thermodynamics and Fluid Mechanics
Phone: +49 3677 69-2445
Mail: christian.cierpka@tu-ilmenau.de