When spins go shopping
For the information carriers of the future, effective spin transport is vital. Researchers from the FOM Foundation and the University of Groningen saw hopeful results at the start of 2012 in experiments with channels of graphene. Now they have developed a model that also explains those experiments and provides possibilities for influencing the spin dynamics. They will publish their model on 6 February in the renowned journal Physics Review Letters.
Spintronics is about materials in which the spin (the magnetic moment) of an electron can move without changing. Only then is it possible to use the spin for ICT applications. However the challenge is to find conducting materials in which the spins have a long lifespan, even though spins ‘live’ for the longest in so-called localised states in non-conducting materials.
The Physics of Nanodevices group (based in Groningen) of FOM workgroup leader professor Bart van Wees had already discovered that electron spins in conducting graphene channels on a substrate of silicon carbide with a non-conducting buffer layer in between, lived longer than they had expected based on the properties of the conductor. This enhanced spin dynamics has now been explained by a new model produced by FOM PhD researcher Thomas Maassen MSc and his colleagues within the European Concept Graphene partnership.
Buffer layer
The explanation was found to lie in the buffer layer between the graphene channel and the substrate. In this graphene-like buffer there are localised states in which the electron spins remain for some time. The researchers use the analogy of a busy shopping street. A person will need a certain amount of time to walk through this street. However, if he goes into different shops then the total amount of time needed will increase. Similarly electron spins move more slowly through a system if it contains localised states where they can remain for a while. The researchers verified the model by repeating the experiment without the buffer layer and therefore without the presence of localised states. Just like the model predicted, a system without a buffer layer was found to have no effect on the spin dynamics.
Sensor
In effect the spin state at the end of the graphene channel provides information about the localised states around the channel. If you were to deliberately introduce such states into the system by adding certain molecules then the system would become a sensor with which you could gain more information about these molecules. Ultimately this concept could even be used in future information carriers to allow the spin states in a crystal lattice to 'talk' to each other.
Contact information
Thomas Maassen
+31 (0)50 363 48 80
Jasper van den Berg
+31 (0)50 363 48 80
Bart van Wees
+31 (0)50 363 49 33
Reference
'Localized States Influence Spin Transport in Epitaxial Graphene'. T. Maassen, J.J. van den Berg, E.H. Huisman, H. Dijkstra, F. Fromm, T. Seyller, B.J. van Wees.
Physical Review Letters, Volume 110, issue 6 067209 (2013).