Dynamics in one-dimensional spin chains newly elucidated

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.