Superconducting nanostructure first step towards Majorana fermion
An international team of researchers has succeeded in making the surface of a so-called topological insulator superconducting by placing it in between two superconducting electrodes. This nanoscale sandwich construction is an important step towards the discovery of a new particle: the elusive Majorana fermion. The researchers from the MESA+ Institute for Nanotechnology at the University of Twente, the Foundation for Fundamental Research on Matter, the High Field Magnetic Laboratory of Radboud University Nijmegen, Leiden University and the Institute for Superconducting and Electronic Materials of the University of Wollongong (Australia) published their results on 19 February 2012 online in the journal Nature Materials.
Topological insulators and superconductors are two very unusual electronic materials. Topological insulators insulate on the inside but conduct on the surface. Furthermore, they have the unusual property that the spin (the magnetic moment) of the charge carriers is linked to the direction of their movement. In superconductors electric current experiences no resistance whatsoever. To make topological insulators superconducting, the researchers in the MESA+ Nanolab created a special nanostructures: two superconducting electrodes with the topological insulator in between. The superconducting current can move from one superconductor to the other via the topological insulator's surface.
High magnetic fields and low temperatures
If two superconductors, separated by another material, are brought very close together then a structure arises with exceptional characteristics: the Josephson junction. Current can flow through the non-superconducting material without experiencing any resistance and is highly sensitive to a magnetic field. These structures are therefore important building blocks for superconducting electronics and sensors. The researchers have now demonstrated a new Josephson junction, made from the topological insulator bismuth-telluride and the superconductor niobium. By combining measurements made under the very high magnetic fields in the HFML in Nijmegen with electrical measurements at very low temperatures in Twente, the researchers demonstrated that the topological insulator was indeed superconducting at the surface.
Majorana fermion
If the intermediary material in a Josephson junction is a topological insulator then another unusual phenomenon can arise: a Majorana fermion. In 1937, Ettore Majorana predicted the existence of this particle, which is its own antiparticle. Some researchers claim that most of our universe could consist of these particles, although its existence has yet to be demonstrated. However, with the emergence of nanotechnology and topological insulators it might now be possible to artificially produce this particle. Scientists are already thinking of applications of the Majorana fermion as the basis of the quantum computer.
Reference
'Josephson supercurrent through a topological insulator surface state', M. Veldhorst1, M. Snelder1, M. Hoek1, T. Gang1, V.K. Guduru2, X.L. Wang3, U. Zeitler2, W.G. van der Wiel1, A.A. Golubov1, H. Hilgenkamp1,4, and A. Brinkman1
1MESA+ Institute for Nanotechnology, University of Twente, 2High Field Magnet Laboratory, Institute for Molecules and Materials, Radboud University Nijmegen, 3Institute for Superconducting and Electronic Materials, University of Wollongong, Australia. 4Leiden Institute of Physics, Leiden University.
Contact
Prof. A. Brinkman (University of Twente), +31 (0)53 489 31 22.