DFT+mu: a step change in muon spectroscopy

Lead Research Organisation: Durham University
Department Name: Physics


Muon spectroscopy is a powerful experimental technique in condensed matter physics. It involves using the muon, a subatomic particle, as a microscopic magnetometer that we implant into matter, in order to probe the local environment. Use of the muon technique has led to a large number of key advances in our knowledge of quantum magnetism, unconventional superconductivity, semiconductor physics, charge transport and dynamical processes in solids. Despite its clear successes, questions about the validity of muon spectroscopy are still regularly raised, owing to our lack of knowledge of the site of the stopped muon in the solid and the influence that the charged muon probe has on its local environment. This is especially important in a number of high profile cases in which the muon measurements reveal effects that have not been observed with other techniques. In the last two years, we have shown that it is possible to accurately calculate the properties of muon stopping states using pioneering methods based on electronic structure calculations. Although our initial results are very promising, the techniques remain in their infancy and generally approximate the muon as a classical, rather than as a quantum mechanical, particle. We now propose to develop the methods, fostering a quantum mechanical approach, in order to address a range of important, current problems in condensed matter, including superconductivity, frustrated and low-dimensional magnetism and topological phases. Our results will not only dramatically improve a key experimental technique for studying advanced materials, but will directly contribute to research into new materials.

Planned Impact

{Knowledge impact: scientific}
The work will significantly advance the use of the muon-spin relaxation technique in condensed matter physics, materials science and chemistry. Immediate and significant impact will be achieved for scientists studying magnetism, superconductivity and topological physics.

{Knowledge impact: technical}
This proposal therefore aims squarely at developing and rolling out more advanced materials modelling methods and thereby enabling further research into materials likely to have economic impact. New functionality developed in solving the muon stopping states problem will be implemented within the CASTEP materials modelling code in order that the technical advances impact as widely as possible.

{People and training}
We will train two PDRAs in the use of modern computational methods and the use of facilities techniques. Both will benefit from the diverge range of techniques we will employ as part of this project.

{Economic impact and IP}
IP generated in the course of the project will be identified and protected with the assistance of the knowledge transfer services from the three institutions involved.


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Description We have been able to locate the stopping sites of implanted muons in a number of topical materials. This allows us access to key insights from our experimental data on materials with unusual magnetic states such as skyrmion hosting systems. In addition to this we have been able to assess the degree of distortion that the muon probe introduces to materials. In spin chain compounds we have shown that the muon introduces a significant distortion, and based on our calculations we have shown how these distortions lead to a state with sensitivity to the local magnetism. We have also been able to assess and compute the quantum mechanical effects in a number of favourable cases and compare against experiment. Many of these advances have been incorporated into a piece of software that is freely available to the research community.
Exploitation Route These findings will be used to interpret future muon spectroscopy measurements and, more generally, understand the interactions of impurities in magnetic crystals - a field with important technological potential. We plan to start an new PhD project to further develop the quantum mechanical aspects of the research. We have initiated collaborations with the group in Parma, Italy who are carrying out related work, in order to make future advances in a collaborative project.
Sectors Chemicals,Electronics,Energy

Description ISIS Facility development studentship
Amount £39,879 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 10/2016 
End 06/2020