Negative muon spin rotation and relaxation on superconducting MgB₂

The internal nuclear magnetic field in a superconducting MgB2 powder sample was studied with a mu-SR technique. Although the past mu+SR study on MgB2 reported the appearance of a dynamic behavior even below T-c due to mu(+) diffusion, mu-SR shows a static behavior in the whole temperature range measured, as expected. The ZF-mu-SR spectra do not suggest any appearance of additional magnetic field below T-c within the experimental accuracy. Considering the small asymmetry of the mu-SR signal, it is a challenge to detect the appearance of an internal magnetic field below Tc caused by the time reversal symmetry breaking.