Exploring the limits of quantum mechanics
With their dimensions reduced down to the nanoscale, conventional materials assume strange, unfamiliar properties. This is the realm in which scientists expect the unexpected – and where many laws of classical physics no longer apply. Matter observed at quantum scales begins to exhibit properties associated with both particles and waves. The physics behind these properties, known as quantum mechanics, is a field in which tangible progress is now being made. Far from being an obscure theoretical area of science, research in this area is now being applied to a number of mainstream applications. At the Norwegian University of Science and Technology, a research group investigating quantum condensed matter theory and headed by Professor Jacob Linder is seeking to explore the theoretical quirks of quantum mechanics. “In quantum condensed matter physics, you encounter various phases of matter,” he explains. “Classically you have only three: solid, gas and liquid. But when you study quantum physics, this classification of matter becomes more complicated. For instance, not all solid materials behave in the same way. You can have solid materials that are superconducting, and you can have solid materials that are magnetic. These attributes cannot be explained by classical physics, but are rather explained by quantum mechanical effects. They are thus described as quantum phases of matter.” It is these quantum phases that the group seeks to delve into at a theoretical level, and Linder believes they can ultimately stimulate the creation of radically improved new technologies and devices. The team, located in Trondheim, consists of Linder, one postdoctoral researcher, two PhD candidates, and six MSc students. A major theme of Linder’s research is the merging of spintronics with superconductors. Conventionally, superconductivity has been regarded as incompatible with magnetism, and thus spintronics. The zero-resistance encountered in superconductors is normally possible due to electrons being paired up into what are called ‘Cooper pairs’. In these pairs, one electron traditionally has its spin up while the other must be down. Pass a Cooper pair through a magnet, however, and one of the two electrons will inevitably have the opposite spin orientation compared to the magnetisation direction, leading to the destruction of Cooper pairs and thus the loss of superconductivity. However, recent research has suggested that it is possible to retain the Cooper pair and thus superconductivity, with parallel spin electrons by controlling the magnetisation properties of magnetic materials. “If you create artificial structures which combine superconducting and magnetic materials together at the quantum scale, superconductivity will adapt to the presence of magnetism,” explains Linder. “This is very important, since superconductivity allows for the transmission of a current without any resistance. Without superconductivity, spin currents will encounter resistance when passed through materials, which leads to heat and energy loss. But, if you can successfully combine magnetism with such a material – and experimental work exists which shows this is viable - you create the possibility of realising ‘spin currents’ with strongly reduced energy dissipation.” Linder has, together with a collaborator from Cambridge University, recently written a review article in Nature Physics on the topic of superconducting spintronics [Nature Physics 11, 307–315 (2015)]. To read the full story, visit http://www.projectsmagazine.eu.com/randd_projects/exploring_the_limits_of_quantum_mechanics(opens in new window)
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