Dynamics in one-dimensional spin chains newly elucidated
The data from neutron scattering (left) provide information about absorbed energies in reciprocal space. With the new evaluation, it has been possible to obtain statements about new magnetic states and their temporal development in real space (right). The colours blue and red indicate the two opposite spin directions. © HZB
Neutron scattering is considered the method of choice for investigating magnetic structures and excitations in quantum materials. Now, for the first time, the evaluation of measurement data from the 2000s with new methods has provided much deeper insights into a model system – the 1D Heisenberg spin chains. A new toolbox is available for elucidating future quantum materials has been achieved.
Potassium copper fluoride KCuF3 is considered the simplest model material realising the so-called Heisenberg quantum spin chain: The spins interact with their neighbours antiferromagnetically along a single direction (one-dimensional), governed by the laws of quantum physics.
"We carried out the measurements on this simple model material at the ISIS spallation neutron source some time ago when I was a postdoc, and we published our results in 2005, 2013 and again in 2021 comparing to new theories each time they became available," says Prof. Bella Lake, who heads the HZB-Institute Quantum Phenomena in Novel Materials. Now with new and extended methods, a team led by Prof. Alan Tennant and Dr Allen Scheie have succeeded to gain significantly deeper insights into the interactions between the spins and their spatial and temporal evolution.
Dynamics like a wake
"With neutron scattering, you sort of nudge a spin so that it flips. This creates a dynamic, like a wake when a ship is sailing through water, which can affect its neighbours and their neighbours," Tennant explains.
”Neutron scattering data is measured as a function of energy and wavevector” says Scheie “ Our breakthrough was to map the spatial and temporal development of the spins using mathematical methods such as a back-Fourier transformation.” Combined with other theoretical methods, the physicists gathered information about interactions between the spin states and their duration and range, as well as insights into the so-called quantum coherence.
New tool box
The work demonstrates a new tool box for the analysis of neutron scattering data and might foster a deeper understanding of quantum materials that are relevant for technological use.
- Porous Radical Organic framework improves lithium-sulphur batteriesA team led by Prof. Yan Lu, HZB, and Prof. Arne Thomas, Technical University of Berlin, has developed a material that enhances the capacity and stability of lithium-sulphur batteries. The material is based on polymers that form a framework with open pores (known as radical-cationic covalent organic frameworks or COFs). Catalytically accelerated reactions take place in these pores, firmly trapping polysulphides, which would shorten the battery life. Some of the experimental analyses were conducted at the BAMline at BESSY II.
- Metallic nanocatalysts: what really happens during catalysisUsing a combination of spectromicroscopy at BESSY II and microscopic analyses at DESY's NanoLab, a team has gained new insights into the chemical behaviour of nanocatalysts during catalysis. The nanoparticles consisted of a platinum core with a rhodium shell. This configuration allows a better understanding of structural changes in, for example, rhodium-platinum catalysts for emission control. The results show that under typical catalytic conditions, some of the rhodium in the shell can diffuse into the interior of the nanoparticles. However, most of it remains on the surface and oxidises. This process is strongly dependent on the surface orientation of the nanoparticle facets.
- KlarText Prize for Hanna TrzesniowskiThe chemist has been awarded the prestigious KlarText Prize for Science Communication by the Klaus Tschira Foundation.