28 August 2022 to 2 September 2022
Science and Technology Campus, University of Parma
Europe/Rome timezone
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Negative muon spin rotation and relaxation on superconducting MgB$_2$

P-THU-42
1 Sept 2022, 17:20
1h 40m
Science and Technology Campus, University of Parma

Science and Technology Campus, University of Parma

University of Parma, Italy
Poster Superconductivity Posters

Speaker

Jun Sugiyama (CROSS Neutron Science and Technology Center)

Description

Although $\mu^+$SR is widely used as a tool for studying a microscopic internal magnetic field in condensed matters over 40 years, the counterpart technique, i.e., $\mu^-$SR is less common for such purpose mainly due to a low counting rate for reaching reliable statistics. However, the recent progress in the beam power and counting system overcame such problem. We therefore started a new $\mu^-$SR project to measure a nuclear magnetic field in hydrogen storage materials and battery materials since 2018 [1].
In order to expand the $\mu^-$SR work, we have attempted to measure the $\mu^-$SR spectra on superconducting MgB$_2$ in ISIS to join the time reversal symmetry breaking business. This is because the past $\mu^+$SR work on MgB$_2$ [2] reported the dynamic change in a nuclear magnetic field even below $T_c=39$ K due to muon diffusion, resulting in difficulty to know the variation of the nuclear magnetic field below $T_c$. From a $\mu^-$SR viewpoint, Mg almost lacks nuclear magnetic moments (since the natural abundance of $^{25}$Mg with $I=5/2$ is 10%), and as a result, the $\mu^-$s captured by Mg feel a nuclear magnetic field formed by surrounding B and could detect the change in it accompanied with the superconducting transition. Note that the natural abundance of $^{10}$B with $I=3$ is 19.9% and that of $^{11}$B with $I=3/2$ is 80.1%. Thus, the $\mu^-$ captured by B should exhibits a fast decay due to its own nuclear magnetic moment, and the corresponding asymmetry will disappear.

[1] J. Sugiyama et al., Phys. Rev. Lett. ${\bf121}$, 087202 (2018).
[2] Ch. Niedermayer et al., Phys. Rev. B ${\bf65}$, 094512 (2002).

Primary authors

Jun Sugiyama (CROSS Neutron Science and Technology Center) Ola Kenji Forslund (KTH Royal Institute of Technology) Ms Elisabetta Nocerino (KTH) Prof. Yasmine Sassa (Chalmers University of Technology) Prof. Martin Mansson (KTH) Dr Adrian Hillier (STFC / UKRI) Dr Katsuhiko Ishida (Riken)

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