September 21, 2015

A team of researchers from ICFO – the Institute of Photonic Sciences in Barcelona, Spain, and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Dresden, Germany, discovered a new way to control domains utilizing terahertz radiation from the unique free-electron laser FELBE at the HZDR. The results of this study have been published in the journal Nature Communications.

Magnetic domains are used to store information in hard drives through their alignment. A long sought-after goal has been to control the domain alignment at high speed. In their experiment, the ICFO and HZDR researchers utilized the unique tunable narrow-band terahertz radiation from the FELBE laser in Dresden to align a novel type of domain consisting of electronic order as opposed to magnetic order found in hard drives. These electronic domains form what is known as orbital order, a phenomena that is not well understood, but found often in so-called correlated solids. In the material studied, lanthanum strontium manganite (La_0.5Sr_1.5MnO₄), the atomic orbitals of the manganese atoms order in zig-zag chains. These chains can form along two directions, leading to two possible domain orientations.

In their joint experiment, the research group led by ICFO Professor Dr. Simon Wall and Dr. Michael Gensch's research group at the HZDR, were able to rotate the orientation of the domains from one axis to the other, contact-free, by merely using the polarization of the incident terahertz pulses. Combining their experimental results with theoretical calculations provided by theorists in the research group led by ICFO Professor Dr. Maciej Lewenstein, they were able to identify the dominant driving force for orbital order in lanthanum strontium manganite (LSMO). The model indicated that in this particular case orbital order is driven by forces generated between electrons as they interact.

Future studies aim at utilizing the high-field high repetition rate terahertz pulses from the new super-radiant TELBE facility in Dresden to reveal details of the ultra-fast dynamics of the alignment mechanism.

Publication:  T. A. Miller, R. W. Chhajlany, L. Tagliacozzo, B. Green, S. Kovalev, D. Prabhakaran, M. Lewenstein, M. Gensch, S. Wall: "Terahertz field control of in-plane orbital order in La_0.5Sr_1.5MnO₄", in Nature Communications 6, 8175 (DOI: 10.1038/ncomms9175)