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.
- Electrocatalysis under the atomic force microscopeA further development in atomic force microscopy now makes it possible to simultaneously image the height profile of nanometre-fine structures as well as the electric current and the frictional force at solid-liquid interfaces. A team from the Helmholtz-Zentrum Berlin (HZB) and the Fritz Haber Institute (FHI) of the Max Planck Society has succeeded in analysing electrocatalytically active materials and gaining insights that will help optimise catalysts. The method is also potentially suitable for studying processes on battery electrodes, in photocatalysis or on active biomaterials.
- Scientists Develop New Technique to Image Fluctuations in MaterialsA team of scientists, led by researchers from the Max Born Institute in Berlin and Helmholtz-Zentrum Berlin in Germany and from Brookhaven National Laboratory and the Massachusetts Institute of Technology in the United States has developed a revolutionary new method for capturing high-resolution images of fluctuations in materials at the nanoscale using powerful X-ray sources. The technique, which they call Coherent Correlation Imaging (CCI), allows for the creation of sharp, detailed movies without damaging the sample by excessive radiation. By using an algorithm to detect patterns in underexposed images, CCI opens paths to previously inaccessible information. The team demonstrated CCI on samples made of thin magnetic layers, and their results have been published in Nature.
- Nanodiamonds can be activated as photocatalysts with sunlightNanodiamond materials have potential as low-cost photocatalysts. But until now, such carbon nanoparticles required high-energy UV light to become active. The DIACAT consortium has therefore produced and analysed variations of nanodiamond materials. The work shows: If the surface of the nanoparticles is occupied by sufficient hydrogen atoms, even the weaker energy of blue sunlight is sufficient for excitation. Future photocatalysts based on nanodiamonds might be able to convert CO2 or N2 into hydrocarbons or ammonia with sunlight.