"Tracking decay positrons in a magnetic field for muon microscope applications" - Journal of Physics: Conference Series, Vol. 2462, 2023 Citation C Young and K M Kojima 2023 J. Phys.: Conf. Ser. 2462 012013 DOI 10.1088/1742-6596/2462/1/012013

In this article, we explored the feasibility of a Muon Microscope designed to enhance positional resolution by tracking positron trajectories back to their source positions. Under the influence of a magnetic field, positrons with trajectory components perpendicular to the field exhibit helical motion due to the Lorentz force. By incorporating special relativity, we analytically determined these trajectories in a uniform magnetic field. Additionally, we assessed more practical scenarios, including the impact of finite detector spatial resolutions and positron scattering from materials along their paths.

Roppongi, M. et al. "Topology meets time-reversal symmetry breaking in FeSe₁₋ₓTeₓ superconductor" Nature Comm. DOI: 10.1038/s41467-025-61651-y. July 2025.

Time-reversal symmetry breaking (TRSB) in magnetic topological insulators induces a Dirac gap in the topological surface state (TSS), leading to exotic phenomena such as the quantum anomalous Hall effect. Yet, the interplay between TRSB and topology in superconductors remains underexplored due to limited suitable materials. Here we employ zero-field muon spin relaxation (μSR) as a sensitive probe of TRSB to map out the electronic phase diagrams of iron-chalcogenide superconductors FeSe1−xTex. For the Te composition x = 0.64 with the highest superconducting transition temperature Tc = 14.5 K, which is known to host a TSS and Majorana zero modes within vortices, we detect spontaneous magnetic fields below Tc distinct from a magnetic order. This signifies a TRSB superconducting state in the bulk, revealing the convergence of unconventional TRSB superconductivity with topologically nontrivial electronic structures in FeSe1−xTex. Given the relatively high Tc and the tunability of the Fermi level through chemical substitution, iron-chalcogenide superconductors offer an intriguing platform for investigating the synergy between topological superconductivity and TRSB. My contribution to this paper was contributing to the muon spin relaxation (μSR) measurements.