Films from the Nanoworld
Stefan Eisebitt uses ultrafast light pulses to turn off or reverse magnetisation
Stefan Eisebitt gets to the bottom of things. He uses ultrafast light pulses to not only examine the properties of matter in their “resting state”, but also to see how the excitement of electrons affects the properties of a material, such as magnetism. Moreover, the 51-year-old experimental physicist aims at manipulating materials on the nanoscale.
Since 2015, Stefan Eisebitt has been one of the three directors of the MBI Max-Born-Institute for Non-Linear Optics and Short Pulse Spectroscopy and a professor at the Technical University Berlin since 2008. After studying at the University of Cologne, where he also received his PhD, his research in Julich, Vancouver, Standford, and, since 2002, Berlin focused on how light pulses change the electronic and magnetic properties of rigid bodies. “The light is absorbed and the electrons are temporarily excited in order to change their molecular state,” says Eisebitt.
The electrons determine whether a rigid body is metallic or semi-conductive, or translucent or not. The state of magnetization depends on the electrons, which in turn are affected by the vibrations of the atoms in the crystal lattice. “We examine these things in the short amounts of time that these electronic movements happen in”, says Eisebitt. They last only very few femtoseconds (millionths of a billionth second). The system is stimulated with a short light pulse and tested with a second. This produces time-independent data or, one could say, short films from the Nanoworld starring electrons as the leading actors. The pulses can also prompt magnetically structured material to demagnetize. Moreover, circularly polarized light pulses can reverse magnetization in a controlled fashion. This is hugely interesting with regard to technology, because it could be used for ultra-fast data storage in hard drives.
This already works in a lab with materials made from gadolinium, but the researchers are not completely clear how the processes work. The use of soft x-rays (XUVs) with a wavelength of only a few nanometers (millionths of millimetres) is essential for clarification. It can be used to transfer electrons “highly accurately” between energy levels and for researchers to spectroscopically determine the magnetic properties of any type of atom.
The short wavelengths of the XUV rays make it possible to create images on a nanometer scale. MBI researchers do this by using x-ray holography. Eisenbitt has also contributed to refining this technology, which is now used not only at the BESSY II in Adlershof, but in x-ray lasers all over the world. Meanwhile, some of these experiments with ultra-short XUV pulses can be conducted without large electron accelerators. "We will be able to do many tests on magnetic switching directly here at MBI,” says Eisebitt. Cooperation with the next-door Leibniz-Institute for Crystal Growth (IKZ) is planned, for example, on researching thin metal oxide layers, which have displayed promising magneto-optical properties.
By Paul Janositz for Adlershof Journal