Picosecond accurate slow-motion confirms oxide materials exhibit considerably faster switching properties than do semi-conductors

 Optical laser flash (red) destroys the electronic order (blue) in magnetite and, within one trillionth of a second, switches the state of the material from insulating to conducting.

Optical laser flash (red) destroys the electronic order (blue) in magnetite and, within one trillionth of a second, switches the state of the material from insulating to conducting. © Greg Stewart, SLAC National Accelerator Laboratory

As part of an international team of researchers, scientists at the Helmholtz Center Berlin (HZB) have observed the switching mechanism from a non-conducting to a conducting state in iron oxide (specifically, magnetite) with previously unrealized precision. This switching mechanism - which, in oxides, proceeds in two consecutive steps and which is thousands of times faster than it is in current transistors - is described in the current epub-ahead-of-print issue of the scientific journal Nature Materials (DOI: 10.1038/NMAT3718).  

Materials that have the ability to switch between being good conductors and being good insula-tors are considered good potential candidates for electronic building blocks – for use in transis-tors, for example. The iron oxide magnetite is the best known representative of this class of ma-terials. At low temperatures, magnetite has insulating properties; at high temperatures, the oxide is a good conductor. This switching mechanism however happens so quickly that it’s been im-possible until now to fully grasp it on an atomic level.

Now, an international team of scientists at LCLS, the US source for ultrafast X-ray light at the SLAC National Laboratory, has managed to freeze the switching mechanism in ultraslow-motion. The researchers were able to document that the transition proceeds in two stages. “The first step involves  the appearance of conducting islands within the insulating material. Thereaf-ter, it takes less than a picosecond (that is, one trillionth of a second) before the atoms re-organize to create a complete metallic grid,” explains HZB’s own Christian Schüßler-Langeheine.

At BESSY II, the HZB operated electron storage ring, Schüßler-Langeheine and his team took care of the work that was necessary in preparation for the SLAC experiment. The insights gleaned from this work provided the basic framework for the SLAC experiment and for its suc-cessful realization.

The experiment, which was conducted in California, involved cooling magnetite to a temperature of minus 190 degrees. In a next step, the oxide was hit with laser light, the energy from which ended up prompting the switching mechanism. In place of a strobe light, the researchers used an X-ray laser pulse to observe the switching mechanism. Only a handful of photon sources in the World have the capabilities of performing these types of picosecond interval time-resolved measurements.
“At the HZB, we are doing research on materials for use in faster, more energy-efficient elec-tronics,” Christian Schüßler-Langeheine says.  “Our experiment confirmed that the switch of an oxide material like magnetite can be incredibly fast. Oxides thus represent an exciting alternative to currently available semiconductors – especially the kinds of materials that also show metal insulator transitions at room temperature.”

The research was conducted jointly by scientists at the SLAC and Stanford University, the CFEL and Hamburg University, Amsterdam, Cologne, Potsdam, and Regensburg Universities, the Dresden-based MPI CPfS, the European Source for X-ray pulses ELETTRA in Trieste, the XFEL in Hamburg, the Advanced Light Source in Berkeley, and the Swiss Paul Scherrer Insti-tute. The samples were prepared at Purdue University.

Link to SLAC Press Release


You might also be interested in

  • 40 years of research with synchrotron light in Berlin
    40 years of research with synchrotron light in Berlin
    Press release _ Berlin, 14 September: For decades, science in Berlin has been an important driver of innovation and progress. Creative, talented people from all over the world come together here and develop new ideas from which we all benefit as a society. Many discoveries – from fundamental insights to marketable products – are made by doing research with synchrotron light. Researchers have had access to this intense light in Berlin for 40 years. It inspires many scientific disciplines and is an advantage for Germany.

  • New road towards spin-polarised currents
    Science Highlight
    New road towards spin-polarised currents
    The transition metal dichalcogenide (TMD) series are a family of promising candidate materials for spintronics. A study at lightsource BESSY II has unveiled that in one of those materials even simple linear polarised light is sufficient to selectively manipulate spins of different orientations. This result provides an entirely new route for the generation of spin-polarised currents and is a milestone for the development of spintronic and opto-spintronic devices.
  • BESSY II resumes operation after a long shutdown
    BESSY II resumes operation after a long shutdown
    On 30 August, BESSY II ligth source will resume user operation: the research centre will then welcome guest researchers from all over the world and support them in their various experiments. The 14-week  shutdown was the longest in BESSY II history. Among other works, the main supply was completely renewed. The successful completion of the work was celebrated with all those involved.