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 The research has led to a systematic investigation of methods to compute the muon stopping site in materials and analyse its influence on the physics measured in a muon-spin relaxation experiment. We have developed a suite of methods which have been made available via an innovative and useful piece of software. We have used these methods to evaluate the muon stopping site in a wide range of materials of current interest and this has enabled several insights into the nature of the state of the stopped muon. We have developed and tested several approaches to the specifically quantum-mechanical effects at play and used these to investigate a number of key features in the experiment. These results are now being used across the field and the methods and approaches developed have promise to be widely adopted.
Exploitation Route The suite of programmes can be downloaded and used by other researchers. We are continuing to develop the quantum mechanical aspects of the work through a PhD studentship funded jointly by STFC-ISIS. The use of the methods in a series of high-profile publications has provided publicity and a demonstration of the methods that are now becoming widespread. We have also sought to collaborate with other world-leading groups in the field and are planning joint work on a topical problems enabling us to compare a build on our different approaches to the wider problems related to the research.
Sectors Chemicals,Electronics,Energy

URL https://gitlab.com/BenHuddart/mufinder
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