DFT+mu: a step change in muon spectroscopy

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.

{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.