IMX Seminar Series - Probing singlet states in frustrated magnets with muons

The technique of muon-spin rotation (μSR) has emerged as one of the most important spectroscopic techniques in condensed matter physics, used to study everything from superconductors to skyrmions. As I will describe, it is now possible to understand the interaction between the muon and its neighbouring spins in quantitative detail to probe entanglement and decoherence [1] and to characterise the muon site in many different materials with high accuracy [2,3]. An outstanding problem is that many magnetically frustrated systems exhibit what is known as persistent spin dynamics (PSD) in μSR experiments, the origin of which has remained mysterious since their discovery in the 1990s. As the temperature is lowered, the muon-spin relaxation rate rises (as would be expected for the slowing-down of spin fluctuations) but this rate then saturates at low temperature. To explain this phenomenon, I will describe how muons can couple to singlet states [4] and how this can be extended to understand the way muons couple to a variety of systems exhibiting highly frustrated magnetism. μSR experiments are usually carried out without resonance, but I will describe a new project which aims to use insights from magnetic resonance and include them into μSR, thereby extending the reach of the technique.
References:
[1] J. M. Wilkinson and S. J. Blundell Phys. Rev. Lett., 125, 087201 (2020)
[2] S. J. Blundell and T. Lancaster Appl. Phys. Rev., 10 , 021316 (2023)
[3] P. Bonfà, I. J. Onuorah, F. Lang, I. Timrov, L. Monacelli, C. Wang, X. Sun, O. Petracic, G.Pizzi, N. Marzari, S. J. Blundell, and R. De Renzi, Phys. Rev. Lett. 132, 046701 (2024)
[4] S. J. Blundell J. Phys.: Conf. Ser., 2462, 012001 (2023)

Bio: Stephen Blundell is a Professor of Physics in Oxford University, working in the Department of Physics, and based in the Clarendon Laboratory. He studied physics at Cambridge University, but moved to Oxford after his PhD. He is also a Professorial Fellow of Mansfield College, Oxford and is the author of several textbooks on different aspects of physics. His research focusses on using muon-spin rotation to study a range of organic and inorganic materials, particularly those showing interesting magnetic, superconducting, or dynamical properties. Recently he has been developing a technique called DFT+μ for understanding muon sites, and is building a capability to use radio frequency and microwave pulses to control the muon spin during muon-spin rotation experiments.