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Supercomputers without waste heat

A collaboration at the University of Konstanz between the experimental physics group led by Professor Elke Scheer and the theoretical physics group led by Professor Wolfgang Belzig uses an approach based on dissipation-free charge transport in superconducting building blocks. Magnetic materials are often used for information storage. Magnetically encoded information can, in principle, also be transported without heat production by using the magnetic properties of electrons, the electron spin. Combining the lossless charge transport of superconductivity with the electronic transport of magnetic information -- i.e. "spintronics" -- paves the way for fundamentally novel functionalities for future energy-efficient information technologies.

The University of Konstanz researchers address a major challenge associated with this approach: the fact that in conventional superconductors the current is carried by pairs of electrons with opposite magnetic moments. These pairs are therefore nonmagnetic and cannot carry magnetic information. The magnetic state, by contrast, is formed by magnetic moments that are aligned in parallel to each other, thereby suppressing superconducting current.

"The combination of superconductivity, which operates without heat generation, with spintronics, transferring magnetic information, does not contradict any fundamental physical concepts, but just naïve assumptions about the nature of materials," Elke Scheer says. Recent findings suggest that by bringing superconductors into contact with special magnetic materials, electrons with parallel spins can be bound to pairs carrying the supercurrent over longer distances through magnets. This concept may enable novel electronic devices with revolutionary properties.

[...] "It is important to find materials that enable such aligned electron pairs. Ours is therefore not only a physics but also a materials science project," Elke Scheer remarks. Researchers from the Karlsruhe Institute of Technology (KIT) provided the tailor-made samples consisting of aluminium and europiumsulfide. Aluminium is a very well investigated superconductor, enabling a quantitative comparison between theory and experiment. Europiumsulfide is a ferromagnetic insulator, an important material property for the realisation of the theoretical concept, which maintains its magnetic properties even in very thin layers of only a few nanometres in thickness as used here. Using a scanning tunnelling microscope developed at the University of Konstanz, spatially and energetically resolved measurements of the charge transport of the aluminium-europiumsulfide samples were performed at low temperatures. Contrary to commercial instruments, the scanning tunnelling microscope based at the Scheer lab has been optimized for ultimate energy resolution and for operation in varying magnetic fields.

Journal Reference:
S. Diesch, P. Machon, M. Wolz, C. Sürgers, D. Beckmann, W. Belzig, E. Scheer. Creation of equal-spin triplet superconductivity at the Al/EuS interface. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-07597-w

Original Submission