15 February 2018
A comparison of the theoretical calculations (top row) and inelastic neutron scattering data (bottom row) shows the excellent agreement between the two. The three figures represent different slices through the four-dimensional scattering volumes produced by the electronic excitations.
(Credit: Argonne National Laboratory)
An international team of scientists have utilised the UK’s neutron and muon source, the ISIS facility, to study the structure of electrons in useful materials – such as those with superconductivity or magnetism.
In certain materials, electrons interact with each other very strongly – these are known as strongly correlated electron systems. These materials can have useful properties such as superconductivity or magnetism, and scientists have been studying how such electrons behave for more than five decades to try to unlock their secrets.
The experimental techniques often used to study electrons, such as photoemission spectroscopy, have limitations, but until recently it was not thought to be feasible to measure the electronic structure of materials with correlated electrons using neutrons.
But now, a team of researchers led by the US Department of Energy’s Argonne National Laboratory have demonstrated that neutrons are the perfect tool for this task. They used neutron scattering to see how electrons behave at high or low temperatures – and compared these results to the theoretical predictions.
The team used the Merlin instrument at the Science and Technology Facilities Council’s ISIS facility, and STFC scientist Dr Devashibhai Adroja said: “Merlin was the perfect piece of equipment for this experiment because it is designed to study the behaviour of electrons in correlated materials like these.
“Neutron scattering is vital because it can comprehensively witness the electrons interacting in four dimensions, making it the only technique able to create results which can be compared to the theoretical calculations.”
The research shows that it is now possible to theoretically model even extremely complex systems of electrons. This work indicates it is possible to predict the properties of certain materials – making it much easier to find ways to exploit these useful metals.
Dr Ray Osborn, a senior scientist at Argonne, said: "Neutrons are absolutely essential for this research. Neutron scattering is the only technique that is sensitive to the whole spectrum of electronic fluctuations in four dimensions of momentum and energy, and the only technique that can be reliably compared to realistic theoretical calculations on an absolute intensity scale."
The researchers compared the four-dimensional measurements taken using the neutron scattering technique with a model previously calculated by computer and found they were remarkably close.
This means the gap between the experimental results and theoretical models are becoming narrower which means computer simulations could soon be a vital tool in discovering new materials and probing their uses through materials engineering.
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