18 September 2015 Controlling material properties

Orbital domain structure in LSMO

THz pulses reveal driving force for orbital order in correlated solids. 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 THz radiation from Europe’s only quasi-cw THz free electron laser FELBE. 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, and a long sort-after goal has been the ability to control the domain alignment at high speed. In their experiment, the researchers utilized the unique tunable narrow-band THz radiation from the FEL 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, La0.5Sr1.5MnO4 (LSMO), the atomic orbitals of the Manganese atoms order in zig-zag chains. These chains can form along two direction, leading to two possible domain orientations.

In their experiment, ICFO researchers Dr. Timothy Miller and ICFO Professor Simon Wall, in collaboration with the research group led by HZDR Professor Michael Gensch, 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 THz pulses. Combining their experimental results with theoretical calculations provided by ICFO theorists Dr. Ravindra Chhajlany, Dr. Luca Tagliacozzo, and ICREA Professor at ICFO Maciej Lewenstein, they were able to identify the dominant driving force for orbital order in 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 THz pulses from the new superradiant THz facility TELBE in Dresden to reveal details of the ultra-fast dynamics of the alignment mechanism.