Toward new frontiers : Encounter and synergy of state-of-the-art astronomical detectors and exotic quantum beams

Program B01-2	Negative muon capture process of electronic many-body effect in strongly correlated electron system
Principal Investigator	HIGEMOTO, Wataru (Japan Atomic Energy Agency (JAEA)/Tokyo Tech)

Electron correlation in many-body system is one of the central issue for material research. In many systems, electron correlation induces a drastic change of electronic state and very often causes a phase transition. For example, a metal-insulator transition is seen in several transition metal oxides in which, although metallic state is predicted by band theory, insulating state is realized due to strong electron correlations. The nature of electron correlation in many-body system is very complex and it is quite difficult to elucidate the phenomena. To understand the origin of such a phase transition, study of the electronic state itself is crucial. However, it is not easy to determine electronic state in particular at deep inside of material.

Fig. 1. Negative muon capture ratio and electronic state. We study electronic state in many body-electron system by using negative muon characteristic X-ray (“Muonic X-ray”). The muon capture probability for each element in a material (capture ratio) can be estimated from muonic X-ray measurements. Today it is known that the initial process of muon capture depends on the electronic state, structure, molecular structure etc. For example, there are differences in the per-atom muon capture ratio for several transition metal oxides, probably due to the difference of valence numbers. Up to now, relation between phase transition and muon capture have not known at all. We investigate the relation between muon capture processes, in particular muon capture ratio and electronic state in the different phases in well characterized materials.

Members

Reference Materials

• W. Higemoto, S. R. Saha, A. Koda, K. Ohishi, R. Kadono, Y. Aoki, H. Sugawara, H. Sato, “Spin-triplet superconductivity in PrOs₄Sb₁₂ probed by muon Knight shift,” Phys. Rev. B 75, 020510-1–4 (2007).
• W. Higemoto, T. U. Ito, K. Ninomiya, T. Onimaru, K. T. Matsumoto, T. Takabatake, “Multipole and superconducting state in PrIr₂Zn₂O probed by muon spin relaxation,” Phys. Rev. B 85, 235152 (2012).
• W. Higemoto, Y. Aoki and D. E. MacLaughlin, “Spin and time reversal symmetries of superconducting electron pairs probed by the muon spin rotation and relaxation technique,” J. Phys. Soc. Jpn. 85, 091007 (2016).
• W. Higemoto, R. Kadono, N. Kawamura, A. Koda, K. M. Kojima, S. Makimura, S. Matoba, Y. Miyake, K. Shimomura, P. Strasser, “Materials and life science experimental facility at the japan proton accelerator research complex IV: The muon facility,” Quantum Beam Sci. 1(1), 11 (2017).
• K. Ninomiya, T. U. Ito, W. Higemoto, N. Kawamura, P. Strasser, T. Nagatomo, K. Shimomura, Y. Miyake, M. Kita, A. Shinohara, K. M. Kubo, T. Miura, “Negative muon capture ratios for nitrogen oxide molecules,” J. Radioanal. Nucl. Chem. 319, 767 (2019).