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Durham University

Centre for Materials Physics

Muon Physics

Muons are subatomic particles that act as microscopic probes of magnetism. Using particle accelerators we produce muons that we implant into solids, allowing the investigation of new forms of magnetism and superconductivity on the nanoscale. Current areas of research using muons include: molecular magnets, where we use molecules to build magnets that are two-, one- or even zero-dimensional; superconductors, where we use muons to explore the vortex lattice; and frustrated magnets, where it is not possible to satisfy all of the competing magnetic interactions to find the material's ground state, resulting in exotic, quantum mechanical behaviour.

Using muons to explore quantum magnetism and superconductivity

Muons are subatomic particles which we use as microscopic probes of magnetism and superconductivity. Current projects involve using these particles to investigate novel materials whose ground states are reached through a fine balance of interactions. We are interested in recruiting students to investigate several topics with muons.

(i) Molecular magnets are materials whose building blocks are organic molecules. These can be synthesised to have low-dimensional properties, allowing us to investigate physics in two, one, or even zero dimensions. Muons allow us to probe long range magnetic order and the exotic excitations of these systems.

(ii) Frustrated magnets are systems for which it is not possible to satisfy all of the competing magnetic interactions to find the materials' ground state. This often results in exotic quantum mechanical behaviour at low temperatures. These materials, which may be metal oxides or molecular magnets, exhibit a variety of quantum mechanical phenomena which may include the long sought-after spin liquid state.

(iii) Unconventional superconductivity remains one of the most interesting problems in condensed matter physics. We use muons to probe the vortex phase of type II superconductors and measure the superfluid stiffness. We also investigate the interplay of magnetism and superconductivity, which is an important ingredient in understanding high-temperature superconductivity. Current work includes measurements on the recently discovered pnictide superconductors and investigations of molecular superconductors.

Muon-spin relaxation data measured on a molecular magnet.

Further reading

  • Spin-polarized muons in condensed matter physics Contemporary Physics 40, 175 (1999) (arXiv:cond-mat/0207699)
  • Magnetic and non-magnetic phases of a quantum spin liquid F. L. Pratt, P. J. Baker, S. J. Blundell, T. Lancaster, S. Ohira-Kawamura, C. Baines, Y. Shimizu, K. Kanoda, I. Watanabe and G. Saito, Nature 471, 612 (2011)
  • Control of the Competition between a Magnetic Phase and a Superconducting Phase in Cobalt-Doped and Nickel-Doped NaFeAs Using Electron Count D. R. Parker, M. J. P. Smith, T. Lancaster, A. J. Steele, I. Franke, P. J. Baker, F. L. Pratt, M. J. Pitcher, S. J. Blundell and S. J. Clarke, Phys. Rev. Lett. 104, 057007 (2010)